1: A war.
In accordance with prophecy. An extension of the iron of Conquest's Third Law.
It was a warm alliance. FDR and Stalin teamed up in WWII because [heads of Communist countries], and then never stopped. USA + USSR 4 lyf, I guess. (Names not similar by chance, you know.)
They loved each other like sister and brother. As much as Fascists can simulate love, anyway. Had a few spats. Sometimes your toys get broke. A few million worthless peasants die here and there, you know how it goes.
You say FDR's New Deal Republic had a Soviet spy problem? Please. Soviets had a horrible American ideas problem. The Soviets were Owenites. Marx was an Owenite - it's not some weird coincidence he was based in London, that's exactly where you would expect him to be.
The Owenites, of course, were merely taking the Founding Mothers' statements to their logical conclusion. Again, not some weird coincidence they popped up first in America.
Apparently the Russians deeply hate Nazis because Stalin really threw them into the meatgrinder instead of using, you know, strategy or technology or shit like that. (Villeins gonna vill, I guess.) Substantially deadlier than the War of Northern Aggression; not something Americans would really understand. Result: America bought all the way into Stalin's strategic/ass-covering anti-Nazism, because [thoroughly allied], hence America's heretical State Enemy became "white" racists.
As I've mentioned before, Marx's class-based envy wasn't working out anyway. Racial envy: now you're cooking with gas.
P.S. Primarily "black" comes from the fact that ninjas all look the same to Europeans, much like Orientals do. You can tell a Frog from a Kraut from a Limey, but from ninjas it's all overly-excited jibba-jabba, so they only get one word or so. "White" is a legal category, not a race. It was invented for the convenience of the Regressive Inquisition, partly in response to the ninjas, and partly because voters aren't sophisticated enough to handle nuance beyond black and white. Thing good, or thing bad? Ug need Big Man tell Ug what like what not-like. When Ug flee, when Ug hug?
You wouldn't want to confuse poor Ug, would you? He'll run off into the woods if you do, so...