The 20s century was full of dramatic and pivotal moments. But I believe it was the WW1 that opened this Pandora box. It not only has ruined all the idealistic schemes of harmony and peaceful coexistence toward tough-minded realism, but it also paved the way for the so-called redistribution of the world.
The giant empires fell and formation of a new world order started at such an enormous pace, that humanity hardly kept up with it. I think, even today the process is not finished and all the consequences of these 20s century’s hurricanes set off by the WW1 are yet to be revealed.