During the Second World War the US and the USSR were in an alliance to fight the Axis powers in Europe.  The Grand Alliance combined the forces of the United States, Britain and the Soviet Union.  The US and the USSR emerged as the two competing superpowers after victory in May 1945.  The alliance between the superpowers fractured during the wartime conference and the breakdown in relations between 1945 and 1949 led to an era of intense tension, suspicion and confrontation known as the Cold War.  The term refers to the level of hostility in relations which held short of direct conflict due to the rapid escalation of nuclear weapons by both sides  To avoid a nuclear war both powers had to find new strategies to confront and contain each other but avoid escalation. For 45 years of the superpowers dominated international relations and pursued an ideological conflict, a conventional and nuclear arms race, and wars fought by proxy on the battlefields of Asia, Africa, and Latin America. It also involved economic rivalry and the development of huge espionage networks, as each side tried to infiltrate the other to discover military and strategic secrets.