What event in 1957 marked the beginning of the Cold War?

The Cold War is often considered to have begun with the end of World War II, but a significant event in 1957 was the launch of Sputnik 1 by the Soviet Union. This was the first artificial satellite to orbit the Earth, demonstrating Soviet technological capability and heightening tensions between the U.S. and the USSR. The launch sparked fears of Soviet dominance in space and led to the U.S. accelerating its own space program, symbolizing the broader ideological and military rivalry of the Cold War.