5. Although Joseph Stalin was not primarily interested in defeating Japan, what seemed to
convince him to join the Allies in this venture?

He was 'persuaded' because Hitler invaded Russia in June of 1941 and broke their non-aggression pact. Germany and Russia had signed a pact to split Poland and this started the war when the Allies declared on Germany. But when Hitler double crossed Stalin he threw his lot in with the Allies (such as they were at that point). Russia did not declare war on Japan until after the first atomic bomb was dropped on Hiroshima, and by that time the war was all but over. Stalin also knew that, near the end, he would not have to commit Russian troops to invade Japan

Explanation:

i think that the answer is 5