Several things lead to the beginning of the Cold War. The meeting at Yalta where the big three met, (Churchill, Roosevelt, and Stalin) where they were to decide and work out the control of postwar Europe. Each leader brought his own concerns to the table.
Churchill hoped to save the British Empire: Stalin intended to protect his borders and rebuild his country. Roosevelt on the other hand sought worldwide spread of democracy and free trade. Where as Stalin and Churchill favored "great powers" controlling spheres of influence. In Eastern Europe and Poland Stalin demanded recognition of Soviet power in Poland, Romania, Bulgaria, Austria, Hungary, and Czechoslovakia. With more and more countries with installed communist governments the Americans and British became worried and told him to back down, but to no success since war was still waging in the pacific. The Splitting of Germany into different sectors, each one controlled by a different country was also a factor. But not so as much as when the British, American and French sectors were brought together to form West Germany and left the Soviets to have the East. The idea was to Unite Germany but instead it forced it farther apart.
The policy of Containment- the restriction of communism to its current border- was the only way to secure peace drove tension higher. Then it came, Churchill gave his speech to the world and put a clear picture in the minds of the people- The West led by the US, would resist any soviet attempts to expand its influence in the world. The Cold War had begun, but yet this was a new kind of war, where the powers would avoid fighting each other directly but would block each others goals around the world. The weapons of the Cold war were those of stockpiling. It became known as the arms race. Each side would manufactured and stockpiled millions of light weapons, chemical, biological, and the worst and most important the Nuclear bomb. The making and us..