Complex sentence: In 1957 the United States government threatened to deny visas to athlete from Communist countries, causing the IOC to threaten to revoke Squaw Valley's right to host the 1960 Games.
Split into simpler sentences: In 1957 the United States government threatened to deny visas to any athletes from Communist countries. In response to IOC declared that it would revoke Squaw Valley's right to host the 1960 Games.