Final answer:
The Soviet Union's invasion that stalled progress toward détente was in Afghanistan in 1979, affecting U.S.-Soviet relations and Middle East regional stability.
Step-by-step explanation:
The progress toward a détente was stalled when the Soviet Union invaded Afghanistan in 1979. The invasion led to high anti-Soviet sentiment in the United States, severely impacting diplomatic efforts such as the SALT II treaty. Tensions in the Middle East were further exacerbated by this conflict, especially as the Soviet Union aimed to strengthen its influence by supporting Marxist regimes in the region and preventing a pro-U.S. government from emerging in Afghanistan. This invasion also directly led to the United States supporting anti-Communist resistance groups, including the Mujahideen, which would have significant geopolitical consequences for the world and especially for the future of Afghanistan itself.