International alliance is a formal agreement between two or more mostly sovereign states that commits them to work together in some way. They are typically categorized as political unions or military alliances, although some have objectives in several different areas.
The earliest examples of international alliances were military coalitions, created in the wake of major conflicts. They were based on the ancient Indian military theory of Artha-shastra, formulated by the adviser to the Indian king Chandragupta (reigned c. 321–c. 297 bce). It holds that, in a threatening situation, an alliance of friendly states is stronger than one state alone.
The modern incarnation of this concept was developed in the aftermath of World War II by the founding of NATO and the European Union. In both cases, countries joined in order to collectively defend themselves against potential aggressors and to gain economic benefits, such as trade and access to natural resources.
Many members of these alliances also take on faraway missions to help reduce human suffering and address other threats, such as climate change. The Evaluating a Source lesson explores this evolution of NATO from its origins as a bulwark against the Soviet Union to its current mission in places like Syria and beyond.
As these international alliances grow and evolve, they can impact the internal politics of the member states. For example, they may encourage devolutionary movements by empowering local groups to feel more disconnected from central government and seek greater self-determination. Alternatively, they can create positive synergies within the alliance network as, for instance, when new leadership in Seoul or Manila favors U.S. bilateral relations, which increases the value of the alliance to both partners.