I can respond to the portion about people of German heritage in the United States, but not so much the rest.

German-American identity had been almost wiped out by the 1930's. In the lead up to World War 1 many German-Americans pushed for neutrality and suffered a terrible attack on their character in the public arena. There was a huge public relations battle between the nations of Great Britain and Germany to get America to pick a side, or not pick a side. In the end Great Britain won. German music like the previously popular Wagner was no longer played in public places. Streets and towns with German names were renamed, and many cultural remnants of German heritage was wiped away from America. One famous and silly example was Hamburgers renamed Liberty Sandwiches.

When America finally did declare war on Germany the earlier push for neutrality was viewed as borderline traitorous, and many Germans suffered real attacks in retaliation. One German-American was even lynched and his murderers acquitted. Many Germans changed their names to more Anglo sounding names to avoid reprisals. By the time World War 2 was on the horizon there was little left of "German-Americans" to push for German interests, and many had learned their lessons already.

Only recently has German-American heritage begun to rejuvenate itself.