Nations form relationships with other countries for a variety of reasons—to trade in goods, to solve global problems, and even to learn from each other culturally. These relationships may take the form of formal alliances sealed by treaty, or less-formal partnerships to buy and sell products.
International alliances can be a way for nations to strengthen their security by pooling resources and creating a stronger common front against common threats. They can also be used to gain political or economic advantages over rivals. Historically, alliances have been used as a tool to maintain stability through collective security frameworks like the League of Nations or NATO during the Cold War. But in contemporary times, the emergence of new security challenges like climate change and terrorism have changed how alliances are formed.
The history of international alliances dates back thousands of years, from tribal agreements to more modern state-to-state ententes. The earliest examples are cited in the Indian political classic Artha-shastra, written by the king Chandragupta. In modern times, they can involve anything from trade and diplomatic partnerships to military pacts and joint ventures.
NATO, the world’s largest military alliance, began as a collective defense agreement in 1949 that called for members to protect each other against aggression from the Soviet Union. When the terrorist attacks of September 11, 2001 occurred, NATO invoked Article 5 and launched its first mission outside Europe, Operation Enduring Freedom in Afghanistan. This timeline traces the evolution of this alliance as it expanded its membership and changed its mission to address evolving global threats.