During the Second World War, France, Britain, the United States and the Soviet Union fought together - they were allies. But soon after the Second World War, nations around the world who believed in democracy became allies with the United States and Western Europe. Meanwhile nations who believed in communism became allied to the Soviet Union. The United States and the Soviet Union both began to build huge numbers of powerful weapons, including atomic bombs. The Soviet Union had a special secret police force called the KGB. It was the role of KGB officers to protect the interests of the Soviet Union and collect intelligence about its enemies.