The early 1990s marked the end of the Cold War. During the Cold War, the military strategies of the United States and the Soviet Union were focused on preventing a nuclear war between these two countries.
The two superpowers became involved in third world conflicts, for example, in Vietnam, when doing so was seen as a way of aiding, or halting, the spread of Communism.
After the Cold War, and the dissolution of the Soviet Union, conflicts between third world countries continued to take place. The NATO countries took on the role of "world policeman" during these conflicts.
Countries such as the United States, Great Britain and France continued to modernize their tanks, incorporating new developments in tank design, for example, in reactive armor, weaponry and electronics.
Meanwhile, countries like Iraq and the nations of the former Yugoslavia continued to rely on old Soviet tanks. This led to conditions of asymmetric warfare during conflicts such as the 1990/1991 Gulf War, in which American Abrams tanks and British Challenger tanks were easily able to defeat outdated Iraqi T-72s. (Weights are in long tons and kilograms.)