The end of the Cold War transformed the global security architecture. It removed a major source of political conflict from the international system and liberated the UN from more than four decades of virtual political paralysis. Popular concerns about the threat of global nuclear war that had fueled a worldwide anti-nuclear movement largely disappeared. The ending of East–West hostilities also meant that both Cold War alliance systems – NATO and the Warsaw Pact – lost their strategic raison d’être. The Warsaw Pact ceased to exist in 1991, while NATO shrank sharply in the 1990s. NATO defense budgets decreased by 30 percent; military force levels by 28 to 40 percent, while US armed forces in Europe shrank by two-thirds between 1991 and 1997 and NATO strategic planners pondered the future of an alliance that had lost its traditional rationale, but had not yet found a new strategic role.

Absent the communist threat that had sustained the alliance for more than forty years, Western policy began increasingly to focus on what appeared to be the growing threat of violent instability in the developing world – and in the Balkans. Less than five years after the ending of East/West hostilities, Saddam Hussein had invaded and occupied Kuwait in an act of gross unprovoked aggression, the break-up of Yugoslavia had led to a savage civil war in Bosnia, the UN peacekeeping mission in Somalia had collapsed in the wake of an abortive US attempt to kill a Somali warlord, and an estimated 800,000 Tutsis and moderate Hutus had been killed in the Rwandan genocide.

In 1990, noted realist scholar, John Mearsheimer, famously argued that the world could come to miss the Cold War.

The end of the Cold War had a major impact on security in the developing world where the overwhelming majority of wars were now being fought.