It was expected that the great powers would work together to keep the peace. Instead, disagreements between the Soviet Union and the West created a state of international tension called the Cold War. The Soviet Union's goal was to spread its Communist system throughout the world. The Western nations, led by the United States, joined together to resist Communist expansion. Both sides built up their armaments, including atomic weapons. Nevertheless, the United Nations has made progress toward world cooperation and has adapted to changing circumstances that were not dreamed of by its founders.