Not all the world violently reduced their ethnic minorities at the point of a gun during and at the end of WWII : only its most civilized portion : Europe !
The whole ideology of Progress, with its claims that the most civilized nations at the top were also the most moral, took another fatal body blow as a result.
Even before WWII formally began, small nations like Poland licked their lips and seized tiny portions of the equally small Czechoslovakia that they claimed - horrors - had a few of their "fellow" ethnics who they discovered had been mistreated by the Slovaks.
(One wonders how many hundreds of nations could invade Canada using the same feeble excuse, seeking to recover their "fellow" ethnics who emigrated to Canada beginning almost 500 years earlier.)
When Poland itself was soon invaded by Germany in turn, using the excuse that it was merely rescuing mistreated ethnic Germans in Poland, the general moral case for humanity helping Poland was neatly undercut.
Poland ended the war kicking out millions of its German residents from the lands to the west of the old Poland while receiving millions of Poles forcibly kicked out of the lands to the east of the old Poland.
Perhaps as many as a million Germans died in this process, mostly the weaker and relatively innocent children and elderly.
Then the Ukraine murderously killed and chased their Poles out of their new nation - a process the new Polish nation did to their Ukrainians in reverse.
This sort of squalid behavior happened all over middle and eastern Europe.
Western Europe and their colonial allies, together with all the neutral nations, refused to stop all this ethnic cleansing and ethnic cleansed themselves in a sense by not taking in many refugees or DPs themselves.
And by knowingly returning the fleeing citizens of the Iron Curtains countries to the non-tender care of their erstwhile Ally, the USSR.
Almost nobody in 1945 protested all this murderous cleansing, because pure nations of one ethnicity only was a widely accepted goal of all civilized peoples - a Godly good.
Seventy five years later, with almost the adults of the civilized world of 1945 dead and buried , it will soon be possible for their children and grandchildren in the former civilized world to stop pretending that only the Nazi Germans practised ethnic cleansing during the time around WWII....