What do you consider the most significant reason for the collapse of detente?

The most significant reason for the collapse of détente was the changing geopolitical landscape, particularly the Soviet Union's aggressive actions in the late 1970s, such as the invasion of Afghanistan in 1979. This move heightened tensions and demonstrated to the United States that the USSR was not committed to peaceful coexistence. Additionally, domestic pressures in the U.S., including a resurgence of anti-communist sentiment and the election of more hawkish leaders, further shifted the focus away from détente, leading to a renewed arms race and increased hostility between the superpowers.