NASA - Apollo-Soyuz: An Orbital Partnership Begins

But by the mid-70s things had changed. The U.S. had "won" the race to the Moon, with six Apollo landings between 1969 and 1972. Both nations had launched space stations, the Russian Salyut and American Skylab. With the Space Shuttle still a few years off and the diplomatic chill thawing, the time was right for a joint mission.