If we are willing to say that a country profitted from the war despite a huge cost, how about the Soviet Union? Before the war they were one of several world powers, all the rest of which were basically anti-Bolshevik although they were not planning to fight over it. The only other Communist country on earth was Mongolia. After the war they were one of just two superpowers. They controlled eastern Europe and had made advances in the Far East. All their European rivals were drastically weakened, and the colonial empires were on the verge of breaking apart. Most of the liberation movements or new governments were Marxist or socialist to some degree. The USSR controlled more territory and had a significantly greater share of world power.