What were the most significant years of the 20th century?

I'm using "change" as in evolved as a society.

The WTC did not evolve, so don't use that as an example.

It evolved into a pile of dirt.

The 1950s evolved into something worse.
I loved the 50s; the 40s had a special charm too.
David

It dissolved into a pile of dirt, not evolved.

Is that what the 1950s did ?

David - you know that I meant the WTC. I'm tiring of your word games.

World War I of course. And all the major events leading up to it should count as well, but since several (especially the congress in Berlin in the 1880's) fall outside of the scope of your question, I wont put them forward. But WWI, and the disastrous peace settlement, was one of the major factors for the rise to power of the NAzi party, resulting in WWII. Furthermore, I'd say part of the succes of the Russian Revolution stems from lack of reaction from the rest of the worldpowers, since they were already in a state of war.
Where before the first World War, Britain was seen as the major world power, during the course of this war, it became abundantly clear that honorific should go to the US of A.
I wont even go into the technological developments that were a result of this war, but they bear mentioning as well.
World War II, by the way, runs a close second.

The cover of Newsweek is pushing for 1968 as the year that made us who we are and, from my own memories and experiences, I'd have to agree. The shifts in culture were incredible.

Most significant years in what sense? who are we asking? there will not be one list that all could agree on. it's situational.

from where i sit
1919 and 1920 - the peace conferences following the WWI that changed the face of Europe
1933- Hitler elected
1939- invasion of Poland, Czechoslovakia split up... puppet Nazi regimes in Slovakia, Croatia, Hungary....
1945 (to 1948) - ethnic cleansing as a response to WWII, forced transfers of over 10 million of Germans, Hungarians, Ruthenians... on the basis of "collective guilt"
1956- crushed revolution of Budapest
1961 - first man in space- Yuri Gagarin
1963 - first woman in space - Valentina Tereshkova
1968 - Prague Spring and the Warsaw Pact Invasion
1976 - three international human rights covenants go into practice - the INternational Covenant on Civil and Political Rights, the Int. Covenant on Social, Cultural, and Economic Rights and the Helsinki Final Act ("basket" 3 that contained human rights provisions and that many see as the beginning of the downfall of the Soviet block)
1989 - Fall of the Berlin wall, Velvet Revolution in Czechoslovakia, fall of communism in Bulgaria, Romania.. Chaushescu executed on Christmas day.
1991-fall of the Soviet Union, dissolution of Yugoslavia

Could the assassination of Archduke Ferdinand be the pivotal event?

http://en.wikipedia.org/wiki/Assassination_in_Sarajevo

Its certainly true that the assassination of Archduke Ferdinand set off a chain of events that has ripples down to our time. It triggered the WW1, that was largely responsible for WW2 which in turn led to the polarisation of the world.

Its a bit like chaos theory, you know the butterfly's wings starting a hurricane. But if Princip had not fired those shots would the world today be different? Not significantly imo. Tthere would have been another trigger to start the war.

I don't think it was the pivotal event. It certainly was the excuse used to start WWI. The underlying issues and tensions had been stewing for several decades at that point, and if the archduke had not been shot, another excuse would have done just as well.

For sure. The time had probably come.

I dare say that it may depend less on general truth than on subjective interpretation. My own view of it consists of World War One (and the ushering of democracy, the four great freedoms) and by far the creation of the international order by the US following the defeat of fascism etc. I agree that the fall of the Soviet Union was a remarkable (historical, political) turning-point of the last century.

1945: the fall of nazism
1991: the fall of communism

I continue my assertion that 1914 is the pivotal year, not only because of the change in the intensity of warfare, but because the entire outlook of civilization began to change from one of hope for the perfectibility of the human race to one of quest for survival.

1917 - The Bolshevik Revolution
1929 - The Great Crash
1945 - Victory of the Democracies
1954 - (May 6th was particularly good)
1968 - Youth movements all around the world - a turning point in social culture.
1989 - Fall of the Soviet bloc

Also:

1960; (approx) Mass availability of the contraceptive pill (at least in most western democracies.)

1960/70 (approx) : Legalising of abortion in most western countries

Late sixties: Second wave of feminism in the west.

1960's: Civil rights movement in the US (also had a profound effect in Australia)

Discovery of antibiotics in the 1930's (effects now attenuating)

Foundation of Israeli state, 1948.

1908.

The first production Model T was built on September 27, 1908, at the Piquette Plant in Detroit, Michigan.

Worthy of a forum all to itself.

Excellent choice.

I'll stick with Archduke Ferdinand.