https://en.wikipedia.org/wiki/Allied_intervention_in_the_Russian_Civil_War

You mean this one? Technically the USA were invited in like vampires by the current official ruler technically to fight rebellion. So "attacked" - no. Sold itself like a mercenary imperialistic scum in some deal to a despotic tsar - definitely.

Oh, and they were barely USian soldiers, it was mostly Europeans. And to be perfectly candid, everything about that intervention is considered to be British brainchild - look at the Korniłow and the support he got from Britain until he failed.

At least that's my take on it.