The Cold War was a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc, which began following World War II. Historians do not fully agree on its starting and ending points, but the period is generally considered to span the 1947 Truman Doctrine to the 1991 Dissolution of the Soviet Union. The term "cold" is used because there was no large-scale fighting directly between the two superpowers, but they each supported major regional conflicts known as proxy wars. The conflict was based around the ideological and geopolitical struggle for global influence by these two superpowers, following their temporary alliance and victory against Nazi Germany in 1945. Aside from the nuclear arsenal development and conventional military deployment, the struggle for dominance was expressed via indirect means such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, rivalry at sports events and technological competitions such as the Space Race.