I'm sorry if this seems like a dumb question, but my history education was severely lacking and there is a lot I don't know

From what I understand, the US and Russia are both capitalist but they both oppose each other, while there seems to be greater cooperation between the US and EU + Britain. Why's this the case? I would extend this question out to China but from what I understand from the struggle sessions is that we don't fully know yet where China stands (feel free to correct me)

Again I'm sorry if this all sounds dumb, I'm very ignorant of history and of the world outside the US