So, it’s a mixture of economics and political influence. The United States became one of the two global superpowers because North America was not a war zone like Europe was. Therefore its infrastructure was left intact, including its manufacturing sector. Britain and the United States were the two largest economies in the world before the Great Depression, but Britain being involved in the war earlier as well as German bombing campaigns resulted in the American economy staying afloat during and after the war. The Soviet economy was unaffected by the great depression because it had cut off most of its ties to the global economy and instead focused on building a socialist state and agricultural collectivization.

Also, while the Soviets and the Americans were allies during the war, both were wary of the other. Harry Truman actually used anticommunist rhetoric to his advantage in order to win the presidential election 1948. Both nations wanted to exert their influence as superpowers upon Europe and the rest of the world, with the United States providing economic stimulus to Western Europe in the form of the Marshall plan, while the Soviets installed friendly satellite states across eastern and central Europe in the wake of the Red Army’s liberation of these countries from the Germans and local collaborators.

So, to answer both questions, the Cold War couldn’t have been between the US and UK because of the personal friendship between Franklin Roosevelt and Winston Churchill, how both of them shared the same goal of the Second World War being a war for democracy and political liberalism, and most importantly the connection between the US and UK consistently being referred to as the “special relationship”. Anglo-American relations are some of the strongest in the world regarding diplomacy and culture, and would be difficult to break down. Furthermore, the UK could not have been one of the global superpowers like it was before the Second World War because of the tarnished state of its economy. Because of the size of their respective economies and the amount of political pressure placed on European allies, the US and Soviet Union became the clear protagonists of the Cold War.