If Napoleon had won the Battle of Waterloo in 1815...

Had Napoleon won the battle of Waterloo, it would simply have meant that he probably would have had what had been offered to him early 1814, which is to say France with her "natural" borders. That would have been modern France, with a sliver of the northwestern portion of Italy, all of what is now Belgium, a sliver of the western portion of what is now Germany, and the southern portion of Holland. Basically, France bounded by the Pyrenees, the Med, the Alps, the Rhine, the North Sea and the Atlantic.

There is no reason to assume that that would in any way have altered the conditions which eventually lead to the First World War, which began in the Balkans. To the extent that a great many other things might not have happened as they did, the exact nature of the Great War and the exact timing might have been different, but it is unlikely that the underlying causes of three Balkan Wars within a a decade (the third one exploding into the Great War) would have been altered.

The reaction of monarchical Europe to Napoleon was the "Holy Alliance" of reactionary powers--Austria, Russia and Prussia. Failing to defeat Napoleon definitively would not have altered their reactionary attitudes (the defeat of the conservative Republicans in the mid-term elections hasn't lessened the rhetoric of reactionary Americans--in fact, it has only become more strident).

The intention of the Austrians to wrest the Balkans from Turkey and to impose their own rule would not have been any different--Napoleon did nothing to change that, his pretensions and use of France's military superiority only delayed the reckoning. The nationalistic idiots in Serbia who dreamed of a "Greater Serbia" at the expense of their neighbors would not have altered. The falling out which made Prussia and Austria suspicious of Russia, and the naked ambition which lead Prussia to impose themselves on the German nation would not have changed. The relative liberalism of England and France which drove them, however reluctantly, to ally with one another to oppose the reactionaries of the Holy Alliance would not have changed.

Had Napoleon won at Waterloo, it likely would only have postponed the day of reckoning. Napoleon's ambition and thirst for power and glory were a disease, eating him up. I doubt that he would have been content just to rule an enlarged France, and i doubt that the French nation would long have willingly sustained a new round of ruinous wars. Europe, basically, had had enough of him. France had been admirably organized to make war, but that doesn't mean that they would have continued to wish to do so. The history of France from 1815 to 1830 was a ludicrous interlude of attempting to re-impose a despised monarchy on a people who would not long tolerate it. The beneficiaries of the Revolution had been the bourgeoisie--and they were not charmed with the return of Bourbon monarchy, and only tolerated it so long as it did not harm their interests. The bourgeoisie tolerated and participated in the uprising of 1830 which rid them of the Bourbons because they derived no benefit from that monarchy, and justifiably saw that monarchy as a hindrance to industrial development and the deployment of new financial and credit instruments which made industrialization possible. The working class and the poor were starving worse in 1830 than they had been in 1789--their grievance was obvious.

I suspect that you wished to ask if the world would have been better off without Napoleon. It is doubtful that much would have changed. The Wars of the Revolution, before Napoleon ever rose to power, had already exported the ideas of the Revolution to the middle class people of Germany and Italy, who were ready to hear the message. The Dutch had already created a middle class republic more than a century and a half before the arrival of the French, whom they already despised as their traditional enemies. The rise of Napoleon served to put an end to the Holy Roman Empire, and his blatant greed and rapaciousness ended any illusions of idealism among the people of Germany and Italy, but the desire of the bourgeois to take control of their own lives, and to push aside archaic, greedy and hindering oligarchy had taken root before Napoleon ever came along.

I don't know why you think anything which happened in France would have "obviated" the First World War. It began in the streets of Sarajevo, not Paris.

If one was to exercise 'what if' history, might the pivotal campaign to russia be a much better vantage point? If he had won that one, or even if he lost it but with far less soldiers lost... Europe would look entirely different.
What the result of a europe pretty much unified under Napoleonitic rule would be for the major conflicts a full century later, I don't know. A lot of the tensions and strains that pretty much forced Europe in the first World War had to do with nationalism and colonialism. If a unified europe would have lasted for a while (highly unlikely, especially after Nappie's death), one of the 'causes' of WWI might not have existed, but if that would have been enough to stop the war?
Besides, who is to say what Napoleon would have done after he had succesfully conquered Europe? I am by no means an expert, but what I know about his persona seems to indicate he had ambition enough for 10. He might have tried to conquer all of Asia, Japan included. He might have tried to invade america. Who knows, a first true world empire would have come into being. And, of course, Nappie stimulated scientific research, especially if it applied to war. His prolonged rule might have stimulated
science in certain areas. But all of this is nothing more then fanciful speculation, and frankly enough, there is enough real research left to be done in the field of history.

If Napoleon had won the battle of Waterloo, he simply would have lost the next battle, or the battle after that. The allies in 1815 had put together an even larger coalition than the one that defeated Napoleon in 1814. Austrian-Allied armies were in the field in central Germany and northern Italy, and Russian troops were on the march from Poland. In contrast, Napoleon's Armee du Nord that he put into the field in 1815 was smaller than his Grande Armee of 1813-1814, and of worse quality too. If Napoleon had defeated the Anglo-Prussian-Allied army in Belgium, he simply would have lost the next battle against the Austro-Russo-Allied army that would have advanced into France through Lorraine.

But you honestly cant rule out that the success of Napoleon at Waterloo would've changed the course of history when it comes to issues such as the First World War; in the aftermath of the 100 days, the congress of Vienna (which was the congress to draw up a map of new europe), this congress not only set up many of the states involved in the Great War, but also pioneered the idea of a european 'Balance of Power', which is where the elaborate system of alliances during the first world war came into existance. On the otherhand; Napoleon's victory would not of changed the rise of German Nationalism in 1848.

I do agree with you though that the turbulance of French politics between Napoleon and the Bourbon restoration would of made Napoleon's success at waterloo negligable in order for him to maintain control, as the people seemed to gain a habit of overthrowing any individual that represented a move back to the 'Ancien Regime' of Autocracy, as demonstrated by the 'White Terror' faction during the 1830's and the overthrow of Charles X.

Although Napoleon's Ambitions after waterloo can be argued, The Great War can be seen to a certain degree as not the fault of Napoleon; The hostility between Russia, Austria, Ottoman Empire and Serbia, as well as the fact that the great war was more a case of dying Empires acting agressively. The Sparks were Lit in Sarajevo, and those were sparks that made the powderkeg of Europe blow into full scale Warfare.