Since the ancient Games were revived in Athens in 1896, few if anyone proposed boycotts during the early decades of this most global of sporting events. Human rights activists in 1936 could have justifiably stigmatized and boycotted the Berlin Olympics. But they didn't, even though Adolph Hitler's persecution of Jews and other minorities and his territorial expansion in Europe had already begun.
The first Olympics boycotted – by Spain, the Netherlands, and Switzerland – were the 1956 Melbourne Games because of the Soviet Union's crushing of the Hungarian revolt. Egypt, Iraq, Cambodia, and Lebanon also boycotted Melbourne because of the Suez War. None of these boycotts had the slightest beneficial effect on the political situations they tried to target.
Many African states threatened or carried out boycotts of the Games in 1972 and 1976 to force officials to ban white-ruled South Africa and Rhodesia (they failed to get New Zealand banned in 1976 because its rugby team had played in South Africa). This aroused sympathy for the athletes banned from competing, but apartheid and white rule weren't affected in the two banned states until years later.