Two reasons why Stalin disliked the United States were, on the one hand, the economic character of the United States as a capitalist nation, with all that this political system implied for the Communists in general and the Soviets in particular. It was thus a nation that was in the ideological antipodes of the position defended by Stalin.
On the other hand, America was the other nation, along with the USSR, that had the most power at the global level: regardless of ideology, the United States was the only nation capable of equaling the Soviets in terms of political, economic and military power. .
