The Space Race was a 20th-century competition between two Cold War adversaries, the Soviet Union and the United States, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the two nations following World War II. The technological advantage demonstrated by spaceflight achievement was seen as necessary for national security, and became part of the symbolism and ideology of the time. The Space Race brought pioneering launches of artificial satellites, robotic space probes to the Moon, Venus, and Mars, and human spaceflight in low Earth orbit and ultimately to the Moon. The competition began on July 30, 1955 when the United States announced its intent to launch artificial satellites for the International Geophysical Year. Four days later, the Soviet Union responded by declaring they would also launch a satellite "in the near future".