<P> The Space Race refers to the 20th - century competition between two Cold War rivals, the Soviet Union (USSR) and the United States (US), for dominance in spaceflight capability . It had its origins in the missile - based nuclear arms race between the two nations that occurred following World War II, aided by captured German missile technology and personnel from the Aggregat program . The technological superiority required for such dominance was seen as necessary for national security, and symbolic of ideological superiority . The Space Race spawned pioneering efforts to launch artificial satellites, uncrewed space probes of the Moon, Venus, and Mars, and human spaceflight in low Earth orbit and to the Moon . </P> <P> The Space Race began on August 2, 1955, when the Soviet Union responded to the US announcement four days earlier of intent to launch artificial satellites for the International Geophysical Year, by declaring they would also launch a satellite "in the near future". The Soviet Union beat the US to this, with the October 4, 1957, orbiting of Sputnik 1, and later beat the US to the first human in space, Yuri Gagarin, on April 12, 1961 . The "race" peaked with the July 20, 1969, US landing of the first humans on the Moon with Apollo 11 . The USSR tried but failed crewed lunar missions, and eventually canceled them and concentrated on Earth orbital space stations . </P> <P> A period of détente followed with the April 1972 agreement on a co-operative Apollo--Soyuz Test Project, resulting in the July 1975 rendezvous in Earth orbit of a US astronaut crew with a Soviet cosmonaut crew . The end of the Space Race is harder to pinpoint than its beginning, but it was over by the December 1991 dissolution of the Soviet Union, after which true spaceflight cooperation between the US and Russia began . </P>

Who was leading the space race in april of 1961