<human>:  What is the history of the NATO alliance?
<bot>: The North Atlantic Treaty Organization (NATO) was formed in 1949 as a mutual defense alliance between the United States, Canada, and several European nations. Its purpose was to create a collective security system to protect against aggression from outside forces and communist expansion in Europe. After the collapse of the Soviet Union in 1991, NATO assumed a new role as a peacekeeping force in the Balkans and other regions. Currently, there are 29 members of NATO with its headquarters in Brussels, Belgium. The latest expansion of NATO was in 2009 when Albania and Croatia became members. Over the past decades, NATO allies have worked together to achieve economic, political, and military objectives that benefit all its members.