The split between Stalin and Trotksy is entirely misunderstood by the professional academics, modern self identifying communist, and well basically everyone besides modern neo-Stalinist whose works have never been translated into English. Understanding Stalins choice to develop socialism domestically is very easy when you factor in his battle against the Communist Party Nomenklatura over who constitued the real final authority in the USSR. Stalin consistently fought to concentrate power in the USSRs state apparatus whereas the nomenklatura wanted the state apparatus to remain an appendage of the communist party. Stalin did not consider the dictatorship of the proletariat to be synonymus with the dictatorship of the Communist Party nomenklatura, he considered it synonymus with the dictatorship of the State Apparatus whose most important posts where by no means staffed by Politburo or Central Committee members. Furthermore Stalin did not want the states most influential officials to be subject to politburo oversight. Basically, Stalin set out to totally sideline the Communist Party in favour of the State Apparatus, and he also intended to have the states top post frequently rotated to prevent mafias from arising. This cost him his life eventually. In short the idea that the real battle was between “socialism in one country” or “permanent revolution” is missing the mark quite a bit. Stalin by no means was against expansionism or spreading the revolution abroad, what he was against specifically was the Communist Party having control over the USSR because he correctly concluded that the parties highest functionaries were a bunch of scoundrels and parasites after years of working with them. The Trotsky formula would be revolution followed with rule by parasites who run the new communist country into the ground whereas Stalin seriously wanted to engage in building states that were actually capable of standing up to the the Capitalist. For anyone actually interested in this topic I wrote a fairly deep dive post about it: https://drlivci.substack.com/p/why-did-the-late-soviet-elite-decide?utm_source=share&utm_medium=android&r=2fizcz