Talk7200 has oversimplified the situation in Germany with regard to the Jews. Initially, Hitler attempted to demonize Communists and all the left wing parties. When the Reichstag was burned, a Dutch Communist (at least, the National Socialists claimed he was a Communist) was alleged to have started the fire. It was sufficient to get the political parties in the Reichstag to either sign on the Hitler's Enabling Act, or to at least keep their heads down during the vote. The Enabling Act allowed the Chancellor (which was Hitler, as the National Socialists have the biggest party, about 35%, although not an absolute majority) to legislate without reference to the Reichstag. That was exactly what Hitler needed to seize complete control of Germany. The conservatives in the Reichstag were already in coalition with the National Socialists, and the Centre Party, a Catholic party voted with the National Socialists on the promise of the removal of all penalties on Catholics in Germany, and quotas of appointments of party members. Hitler was lying, of course, and one of his opponents in the Centre Party advised the leader to get the promise in writing, which he failed to do.
The Reichstag fire took place just a week before elections in the Reichstag in 1933, and Hitler used it as an excuse to suspend civil liberties and the right of habeas corpus. Brown Shirt and SS thugs used intimidation tactics--beating people in the streets, smashing shop windows, sending anonymous threats--to stack the deck. Nevertheless, the National Socialists did not do much to improve their electoral prospects, and even in coalition with the DNVP (the nationalist conservatives), the National Socialists just barely had a majority. So, Hitler rammed the Enabling Act through the Reichstag with the help of the DNVP and the Catholic Centre Party, and called for yet another election (i believe it was the fourth or fifth election in less than a year). The Communists and most left wing parties were banned. Even with the election partially fixed in that manner, the National Socialists still only polled about 45% of the vote.
But the Enabling Act allowed Hitler to ignore the Reichstag, and many of the same people who had supported Hitler were bullied into dissolving their political parties. In July, 1933, all other political parties (other than the National Socialist German Workers' Party, the NSDAP, or Nazis) were banned.
Even in the fixed election in 1933, Hitler did not get a majority. It was obvious that the threat of the "Bolsheviks" didn't have widespread appeal. In a most unfortunate, and unwise move, the Daily Express published an article on a planned Jewish boycott of Germany with the Headline: "Judea Declares War on Germany." Holocaust deniers and Nazi apologists have used this as evidence that the Germans were only responding to a threat from the Jews of the world (insert rolly-eyed emoticon here). Although he probably didn't need any hints, because he was already virulently anti-semitic, Hitler didn't miss the bus on this one. Communists and all leftist parties were already banned or slated for dissolution, and Hitler needed a new boogey man. The Jew as a perfect choice.
Talk7200 is correct that some of the more virulent anti-semites described the Jews as "Christ-killers." This was not necessarily a widely-held point of view, however. The Jews weren't well thought of at all throughout much of their history. In the early years of the Roman Principiate Empire, Jews were seen as trouble makers. Anyone could practice any religion, as long as they gave lip service to the state religion, and at least publicly acknowledged that certain former emperors were "gods." This many Jews refused to do, and so, they were often hunted and persecuted. Early Christians in particular often refused to do this, and to the Romans, Christians were just a sect of the Jews. It was not until long after the life of the putative Jesus that people began to distinguish this particular cult, and they were still seen as Jews. In a famous letter to Pliny, the emperor Trajan advised a "don't ask, don't tell policy." He deplored people who denounced others, but he told Pliny that if anyone refused to publicly acknowledge the state religion, they should be punished--and it applied to anyone.
Of course, the Christian religion was becoming more and more Greek and Roman, rather than Jewish, but not many people outside Christianity acknowledged this. Finally, under Constantine, the Christian religion achieved a high status, and was formally tolerated by the Roman state. (The claim that Constantine himself became a Christian and that it was made the state religion is not, however, supported by the historical record.) Constantine only agreed to this, though, if the Christians were to get their act together, and in the early 4th century, they were deeply divided by what has become known as the Arian heresy. The Bishop Arias and his followers did not agree that the putative Jesus was a god, or a part of god. The church convened a council of bishops at Nicea in 325 CE. This produced the Nicean Creed, which states that Jesus is god (a part of god), and the orthodox canon of scripture was proclaimed.
In the 4th century, no one (as least as far as the historical record is concerned) was calling the Jews "Christ-killers." The formal church establishments of the Roman Catholic, the Byzantine Catholic and the Orthodox churches never endorsed such a point of view. Moreover, in the 3rd, 4th and 5th centuries, Christianity was still largely based in the middle east, and a great many people of the middle east were either Jews, or confessional Jews (i.e., non-Jewish people who practiced the Judaic religion). A great many converts continued to be made among confessional Jews. There was a huge Jewish community in Alexandria, and Alexandria was an early center of Christianity, and more crucially important, of Christian scholarship. Before Christianity began to spread, Jews and Greeks in Alexandria squabbled horribly, often with fatal consequences. A letter is preserved which the Jews of Alexandria sent to the emperor Claudius to complain about the Greeks. But the growing importance of Christianity in Alexandria defused a situation which Roman authorities had never effectively dealt with.
Confessional Judaism had spread because the Aramaeans, who were semitic merchants in the ancient middle east, most of whom became confessional Jews. The Aramaeans were so successful and widespread as merchants in the middle east and central Asia, that they spread Judaism over quite a wide area, and all the way to China. In the early years of Mohammed, before Islam became dominant, most of the Arabs who were not actually pagan were confessional Jews. Some of the books of the bible and most of the Talmud were originally written in Aramaic, and the putative Jesus, if he actually existed, would have been a speaker of Aramaic.
Early in the Christian era, some Christian sects--the Syriac Christian in a modest way, but principally the Nestorian Christians--spread Christianity by following the path of the Aramaean merchants, and appealing to communities of confessional Jews in the middle east and central Asia. The Nestorians were particularly active and successful in the missionary effort. (The relative tolerance--emphasis on relative--of Jews and Christians by early Sunni Muslims directly reflects this.) When Marco Polo in his account of his travels speaks of communities comprised of Saracens (meaning Muslims), Jews, Christians and pagans, he wasn't making things up. The Nestorians followed the Aramaic trail all the way to China, and Polo usually refers to the Christians as Nestorians, and when he speaks of Jews, he is speaking of confessional Jews, not ethnic Jews.
So how did it all go wrong? At the Nicean Council in 325 CE, one minor rule which was made was that bishops and priests were not allowed to practice usury--they were not allowed to lend money at interest. This seemed innocuous enough at the time--the church had not yet grown rich. One good bit of historical evidence that Constantine did not make Christianity the official state religion is that there was no requirement to practice the religion, and no penalty for those who did not. So things ought to have looked good for the Jews.
But the prohibition on usury for bishops and priests was informally, but not officially, extended to powerful men in the Roman state. Aramaic merchants who traded to India and as far away as China were still usually considered Jews by their Asian masters, even if they had become Nestorian Christians. They could freely pass through territories which were murderously hostile to Romans. As merchants, the practice of usury, of lending money, and of carrying letters of credit and other used of credit instruments were commonplace and crucial to good business practice. In the collapse of the authority of the Roman Empire in the West, an important factor was the crippling effects of the latifundia, large slave-driven corporate operations, both corporate farms to produce olive oil, wine and grain, and "factories" full of slaves who made textiles, pottery and other consumer goods. That had a lot to do with the economic collapse in the West (they were not common in the eastern part of the Empire)--and the men who made the system (or rather, fail to work) were members of the class of Equites, the "knights" of the Roman empire.
Romans did not dare travel east of what we think of as Turkey and Syria. With the collapse of the western institution of the latifundia, the Equites increasingly saw the wealth they had accumulated over centuries melt away, and they saw the Aramaic merchants (Jews to them, many were confessional Jews, and many were ethnic Jews--and many had converted to Christianity) piling up the wealth that came for successful trade with the east, and from running informal banks out of their own personal wealth which lent money and provided credit instruments.
Whether actually ethnic Jew, or simply confessional Jews, or even converts to Christianity, the successful merchant class of the eastern portion of the empire were indispensable, and they were hated. Increasingly, Christians of the high classes sneered at "mere merchants," and honor accrued to those who disdained commerce, and who fought for the Empire, or helped to administer it. This ethic was even stronger among the "barbarian" tribes of the West as they converted to Christianity, because they had actually conquered the territory they now ruled, and peasants and merchants were virtually their slaves, for however necessary they were. With the rise of the Lombard "Kings," the authority of the Roman Empire in the west evaporated, at the same time as these Germanic tribes were converted to Christianity--at a time when Romans were coming to despise "Jews" (remember that not all of them were ethnic Jews), and to look down upon money-lending and commerce.
Smart Kings and Princes in the now largely German-dominated West took care of the merchants, and even promoted the more effective of them to important positions at court. For the warrior aristocracy in their domains, this was yet another reason to despise the "Jews" (and once again, many were not Jews at all). Eventually, by custom, Christian merchants were no longer able to lend money or issue letters of credit (except secretly, which they continued to do), and would associate themselves with one or more Jewish merchants in order to facilitate their commercial enterprises. The Germanic aristocracy of these newly conquered lands made a pointed distinction between that the French (actually the Franks were Germans) came to describe as la noblesse de l'épée--the aristocracy of the sword--and la noblesse de la robe, meaning those who became aristocrats because they were administrators to Kings and Princes. This idea was carried to the extreme of "logical" idiocy to the extent that officers in the French Royal Army and Navy needed to be members of the noblesse de l'épée in at least the fifth degree (meaning able to trace no fewer than five generations of ancestors who had been promoted to the nobility for military service).
There was nothing that could be done about Christian merchants, and at any event, commerce was needed, for however much (and idiotically) the nobility despised it. But something could be done about Jews, who were not protected by their religion. Kings and Princes (and Dukes, Counts and Barons, for that matter) who were short of ready money couldn't go to Christian merchants, who wouldn't admit that they had disposable cash, or that they lent money at interest. So they would go to the Jews. If they found it difficult, and eventually, if they simply found it inconvenient, to repay their debts, they might formally deport the Jews in their territory. Of course the duller minds among them, and the cleverest minds, too, saw that it was only necessary to stir up the peasants--dead Jews don't come around to collect their debts. It was in the middle ages of Europe that the "Christ-killer" propaganda became useful, and effective. If the general run of the common people believed (naively) that only Jews lent money, and that only Jews were successful merchants, it was easier to whip up the population against them. It was also easy to create stereotypes of the clever Jews, who although he appeared to be poor, was actually sitting atop a hoard of gold. Many Jews were tortured, raped and murdered because peasants came to believe that all Jews were rich, and hordes of money hidden away. This became a very popular tactic in central and eastern Europe, among Germans, Poles and Russians.
Other Europeans were a little smarter, although all of them turned on the Jews at one time or another. One notable exception was the Venetian Republic, which grew wealthy through trade with the East. Jews and Christians were under certain debilities in the Muslim world, but they were not automatically to be put to death as were pagans. After the beginning of the Crusades, Christians became less popular for obvious reasons. The Jews became the ethnic group of choice for European merchants who wished to trade with the now largely Muslim East. The Doges so valued the Jews, that they gave them their own island in the lagoon of Venice so that they could be protected. The name of the island was Ghetto. Eventually, though, Jews fleeing persecution elsewhere in Europe came to Venice for refuge to such and extent that Ghetto became a byword for poverty and crowding.
In the later middle ages, many European merchants began to ignore the customary ban on usury. It was not against the law, it was just frowned upon. In Germany, the Fugger family, and in Italy, the Lombards began to practice banking, and to issue credit instruments. But the habit of blaming Jews for social ills was tenacious, and even when the issue was not financial, it was convenient to blame the Jews, and to distract the people by urging them to attack the Jews. This was particularly true in Germany, Poland, Lithuania and Russia, but it cropped up in France and England, too. With the Protestant Reformation, many new churches actually admired the Jews, as having made the first covenant with God, but that didn't stand in the way of sound political practice. Now they could turn the population on the Anabaptists (ironically, the ancestors of today's Baptists were accused of living in sin in communes, and practicing free love and satanic rituals--the Protestants did not get along with one another any better than they did with the Catholics).
Into the world of a fragmenting Christianity, the Spanish finally united their two most powerful kingdoms, Arragon and Castile, and behind the banner of Isabella, began the Reconquista, the re-conquest, of Spain from the Moors, i.e., the Muslims. With the final victory in 1492, Ferdinand and Isabella (the King was actually the junior partner) decreed that all Moors (Muslims) and Jews must quit the kingdom, convert to Christianity, or be put to death. Even thought the Church condemned denunciation, the Spanish still practiced an ancient policy whereby a denouncer got half of the estate of a condemned man. The Moriscos (converted Muslims) and the Marranos (converted Jews) were universally despised. Officially known as conversos (the converted ones), the term morisco was a contemptuous reference to Moors, and marranos was derived from the word for swine. A successful conviction of a converso as apostate stood to make the man who denounced them very wealthy. Spain basically drove the Jews from their nation.
It was the grandson of Ferdinand and Isabella, King Carlos, who fought the wars of the Reformation. His mother was the daughter of Ferdinand and Isabella. They had married their daughter (Joan the Mad of Castille) to the son of the Duke of Burgundy, and his mother was Austrian. When the paternal grandfather of Carlos died, the Hapsburg Emperor Maximilian died in 1519, Carlos, by then one of the richest men in Europe (the King of Denmark might have been richer, certainly his grandson was the richest man in Europe in 1618 when the Thirty Years War began, largely due to his stupidity), bribed the German Electors, and got himself elected Holy Roman Emperor. When Martin Luther nailed his 95 Theses to the door of the cathedral, the most bigotted, narrow-minded and bloody-minded monarch in Europe, who was then only 20 years old, was the Holy Roman Emperor. As the Emperor Charles V, he convened an Imperial Diet in 1521, intending to condemn Martin Luther. Luther was escorted to Worms, the seat of the Diet for that session, by German knights, pledged to protect him with their lives--and to kill him if he recanted. Luther managed to escape the clutches of Charles, and the Wars of the Reformation began.
Little wonder if the blood-stained bigot, the grandson of Ferdinand and Isabella, had no time for Jews. In the Wars of the Reformation, the Lutherans hated the Catholics, and Catholics hated Lutherans, but everybody hated Jews, and they were a safe target, for all the same old reasons, and with all the same old excuses. Although he delegated the issue in central Europe (largely Germany) to his brother, Charles was concerned with all the strife, and concluded the Treaty of Augsburg in 1555. That same year, he abdicated in favor of his son Philip, who became the King of Spain, and his brother Ferdinand, who became Holy Roman Emperor (the German Electors were never again going to be so stupid as to elect a man to be Emperor who had the most powerful and wealthy empire at his back).
So, for about three generations, until the outbreak of the Thirty Years War, central Europe knew an uneasy peace. In the latter stages of the Wars of the Reformation, about 1540, John Calvin succeeded in establishing his "godly republic" at Geneva. By the time that the Thirty Years War broke out in 1618, the Lutherans cordially despised the German Reformed Church (who had broken with Luther) and the Calvinists. All of them hated the Catholics, who returned the favor, and just about everybody despised the Anabaptists. But the Jews remained a favorite target, because they were not Christians, and sending the peasants out to kill the Jews didn't piss off any of your Christian neighbors.
The settlement of the Wars of the Reformation--the Augsburg Treaty--and the settlement of the Thirty Years War almost a century later--the Peace of Westphalia--meant that Christians were no longer going to slaughter one another for religious reasons (not without a better excuse). Neither of them said anything about the Jews. During the Thirty Years War, the Puritans had fought three civil wars in England, and Oliver Cromwell ended up as the Lord Protector. He rather liked the Jews, and like all Calvinists, considered that they (the Calvinists) had a new covenant with God, but one which was based upon on the ancient covenant with the Jews. When the monarchy was restored under Charles II, he attempted to emancipate the Catholics, because they had aided his father in the civil wars, and had helped him to escape England in 1651. But the Parliament weren't having any of that. When the Jews of London came to him to complain that English Protestant bully boys were threatening them, he had learned his lesson, and sent some of his boys around to straighten things out for them. Jews may not have had an easy ride in England, but they were never again official proscribed. I doubt very much that there were any Jews left in Spain and Portugal. If there were, they were keeping their heads down. The Jews of Italy managed to actually be accepted, with condescension and contempt, by the Italians. In France, antisemitism remained virulent, but under the surface, and not official--although the Dreyfuss affair showed that it still reached to the highest levels.
At the time that the Thirty Years War began, the King of Sweden, who would become the hero of the German Protestants in 1631, was fighting his uncle, a Swede who had converted to Catholicism to get elected King of Poland. That Swedish King, Gustav Adolf (Gustavus Adolphus as he was known to history), also invaded Russian, and took the Baltic coast from them. Those petty wars were politically motivated (although the Swedes expected him to prevent his now Catholic Uncle from becoming King of Sweden). The Russians had recently driven the Poles out of their nation, and in 1613 had convinced Mikhail Romanov to become the Tsar. Mikhail eventually convince the Swedes that he was not in league with Poland, and Gustav turned to Poland. In 1630, he landed in northern Germany, completely turned the tide of the Thirty Years War, which it appeared the Catholic Austrians had won, and was dead a year and a half later, having first thoroughly defeated and humiliated the Imperialists (the Austrian Catholics and their German Catholic allies). He was succeeded by his daughter, then a toddler, and his chief minister, Oxenstierna, took command of the Swedish forces. The Catholic Cardinal Richlieu of France paid the Lutheran Swedes a good deal of cash to stay in the war with his Catholic Austrian enemies, and the Thirty Years War, which had only notionally been about religion, ground down to a political settlement.
Queen Christina of Sweden, a disaster of a monarch, deeply loved by the common people (how often that has been true in history) eventually grew up, gave away the candy store, and then abdicated so she could go to Rome, convert to Catholicism and annoy just about everybody in town for the rest of her days. Sweden remained Lutheran, the Germans largely remained Protestants of one flavor or another, and the Austrians, Bavarians and Wurttembergers remained Catholics. The Poles remained Catholics, and the Russians remained Orthodox. The Italians remained Catholic, and Louis XIV drove the French Protestants out in 1685 (they went mostly to Holland and Germany, some few went to England). Guess who was left.
So the Europeans, with a certain amount of reluctance, gave up killing one another for religious reasons--unless, of course, one was speaking of Jews. It remained easy to foment antisemitism, and especially violence against Jews, for all of the bad old reasons. This reached its apotheosis with the publication of The Protocols of the Elders of Zion in 1903--which allegedly detailed the Jewish plan to take over the world. Although quickly debunked (even the conservative Times of London eventually condemned the book in 1921), it became and has remained popular among antisemitic Europeans, and enjoyed a particular popularity in Germany. Whether or not Hitler was influenced by it, or simply exploited it, antisemitism and German nationalism were inextricably linked before Hitler was even born, and The Protocols immediately became a best seller among the Germans.
One may allege other reasons why the Jews were persecuted, but basically, they were the perennial outsiders, and others can advance whatever other reasons they wish. Because of their success in business (a situation which the early Christian ethos had helped to create) and their dedication to their religion and to education and hard work made them the target for the envy and spite of Europeans for more than a thousand years. This was particularly true in Germany in the late 19th century, when nationalist movements were almost all also antisemitic. There is no reason to wonder why Hitler made the Jews the scapegoats, one only wonders why he dicked around for so long before he began his campaign against them. The Wannsee Conference in 1942, where Heydrich organized the Final Solution was not a response to the inability to deport the Jews--the Nazis were already killing them, the conference was only organized to do it in a more efficient, faster and less expensive manner than simply shooting them.
