Thus, at a terrible human cost, Stalin’s policies did transform the USSR into a semblance of a modern state by the eve of World War II - “just in time” as it turned out. As described in chapter 40, the USSR bore the brunt of the German war machine. More than 25 million Soviets died on the eastern front, soldiers and civilians alike, and it was through the incredible sacrifice of the Soviet people that the German army was finally broken and driven back. In the aftermath of World War II, Stalin’s power was unshakable. During the war, he had played the role of the powerful, protective "uncle" of the Soviet people, and after victory was achieved he enjoyed a period of genuine popularity, especially as returning Soviet soldiers were given good positions in the bureaucracy.
During the war, the one thing that tied Britain, the US, and the USSR together in alliance was their shared enemy, Germany, not shared perspectives on a desirable postwar outcome besides German defeat. The war required them to work together, however, and that included making compromises that would in some cases haunt the postwar period. In 1943, after the tide of the war had shifted against Germany but well before the end was in sight, the "Big Three" leaders of Britain, the US, and the USSR met in Tehran to discuss the war and what would be done afterwards. There, Stalin insisted that the territory seized from Poland by the USSR in 1939 would remain in Soviet hands: Poland would thus shrink enormously. Roosevelt and Churchill, well aware of the critical role then being played by Soviet troops, were not in a position to insist otherwise.
In 1944, British and American economists met in New Hampshire and devised the basis of the postwar economic order, the Bretton Woods Agreement. That agreement fixed the dollar as the monetary reserve of the western world, created the International Monetary Fund and the World Bank to stabilize the international economy, and fixed currency exchange rates. This plan initially included the Soviets, who would thus be eligible for financial support in addressing the devastation wrought by Germany (as noted below, however, the USSR pulled out in 1948, thereby driving home an economic as well as political divide between east and west).
In January of 1945, when the end was finally in sight and Soviet forces already occupied most of Eastern Europe, Stalin stipulated that the postwar governments in Eastern Europe would need to be “friendly” to the Soviet Union, an ambiguous term whose practical meaning suggested dominance by communist parties. Churchill and Roosevelt agreed on the condition that Stalin promised to support free elections, something he never intended to allow. The leaders also agreed to divide Germany into different zones until such time as they could determine how to allow the Germans, purged of Nazism they hoped, to have self-government again.
In part, Britain and the US gave in to Soviet demands because of the incredible sacrifice of the Soviet people in the war; 90% of the casualties on the Allied side up to 1944 were Soviets (mostly Russians, but including millions of Ukrainians and Central Asians as well). Until 1945, Roosevelt assumed the United States would need Soviet help in bringing about the final defeat of Japan as well. Each side tried to avoid antagonizing the other, especially while the war continued, even though they privately recognized that there were incompatible visions of postwar European reorganization at stake.
Despite those incompatible ideas, many political leaders (and regular citizens) across the globe hoped that the postwar order would be fundamentally different than its prewar analog. Fundamental to that vision was the creation of an official international body whose purpose was the prevention of armed conflict and the pursuit of peaceful and productive policies around the world: the United Nations. The UN was founded in 1945 as a body of arbitration and, when necessary, enforcement of internationally-agreed upon policies, seeing its first major role in the Nuremberg Trials of the surviving Nazi leaders. Its Security Council was authorized to deploy military force when necessary, but its very reason to be was to prevent war from being used as a tool of political aggrandizement. The Soviet Union joined the western powers as a founding member of the UN, and there were at least some hopes that it would oversaw a just and equitable postwar political order.