How did congress try to pressure South Africa into changing its apartheid system

Answer: the American congress imposed sanctions to South Africa

Explanation: In 1986 - about 40 years after the beginning of Apartheid - South Africa's most important commerce partners (the USA, the EC, and Japan) imposed economic sanctions. During the course of the 1985 debt crisis, the time seemed to have come to finally force the Apartheid regime to its knees by economic sanctions.

I Believe The Answer Is Imposing Economics Sanctions.