The 28 African countries boycotted the 1976 Summer Games due to the inclusion of New Zealand in the Games after New Zealand played South Africa in rugby. South Africa had been banned from the Olympics since 1964 due to its apartheid policy and the African countries believed that New Zealand should also be banned for continuing to play South Africa in international sport. When the IOC refused to ban New Zealand, the African countries boycotted.
Go to http://www.sports-reference.com/olympics/countries/USA/summer/1976/BAS/
Ethiopia first participated in the Summer Olympics in 1956 and has been to every Summer Olympics, except the 1976 Summer Olympics, since then.
He only competed in the 1972 Olympics, where he narrowly missed a Silver medal in the 5000 meters. He died in 1975, so he never made the 1976 Summer Olympics.
Montreal and quebec, Canada
The 1980 Summer Olympics were held in Moscow, Russia.