Complex sentence: In 1957 the United States government threatened to deny visas to athletes 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 athletes from Communist countries. The IOC responded with a threat to revoke Squaw Valley's right to host the 1960 Games.