Final answer:
SALT II was not ratified due to the Soviet invasion of Afghanistan in 1979. It raised tensions and ended the détente period, but laid the foundation for future agreements.
Step-by-step explanation:
SALT II was technically killed when the Soviet Union invaded Afghanistan in 1979. Despite efforts to continue with arms reduction agreements, the Soviet action led to heightened tensions and a significant backlash from U.S. lawmakers. This geopolitical event marked a shift in the Cold War-era relations, halting the progress made towards nuclear disarmament at that time. Although SALT II was never ratified, its principles did serve as groundwork for subsequent arms control treaties, like the START agreements that followed in the later years of the Cold War.