Or did World War II make the world free for international Marxism?
Nope. You conflating everything you personally don’t like with Marxism that makes it look that way from your incorrect point of view.
Or did World War II make the world free from God’s laws and the Christian law order that dominated for one thousand years prior?
If your knowledge of history prior to WWII is limited to Christian lands it might look that way but even that is an illusion. Christian law was Roman law with some Christian religious bits stamped on it.
But what if liberal democracy, international cooperation, and multiculturalism imposed upon nations could be just as bad as the Nazis? What about that?
It can’t. The real problem is that you can’t just make a country a liberal democracy, many countries became democracies only to fall back into authoritarian governments of one sort of another because the country and population wasn’t ready.
What if the fundamental problem of Germany was 40 years of dabbling homosexuality, naturalistic evolution, or just good old-fashioned Christian apostasy, and a rejection of Jesus Christ, a national pride, and favoring of traditional civilization rooted in paganism as opposed to God’s law revealed in the Old and New Testaments?
It wasn’t. The Nazis worked with the Protestant churches and the Catholic church during WWII, neither opposed the Nazi in general until it was clear the war was over. The single biggest problem was the Treaty of Versailles was badly written. It both imposed harsh economic conditions on Germany and gave them every reason to get out from under the treaty violently.