International alliances are formal agreements between states in which they undertake to cooperate with each other for mutual benefit. They can encompass a variety of areas and a broad range of objectives, from military alliances like NATO to political unions such as the European Union and economic ones such as trade agreements.

Effective alliances can catalyse national strategy by enhancing force multipliers, which in turn can be a critical source of leverage against adversaries, or by driving economic benefits. They can also act as a backstop against external pressure, such as when an ally’s domestic politics are under strain or they come under threat of a security challenge (as the UK experienced in the aftermath of the Salisbury poisonings).

The value of alliances has long been perceived by governments and the public to be multifaceted. Alliances are often seen as a tool for pursuing global interests, a way to protect local economies, and even as expressions of shared values and principles.

However, the utility of alliances can be eroded by cost considerations. Countries can incur significant costs by participating in an alliance, particularly if its mandate goes beyond defence or is expanded to include peacekeeping missions and other activities. They can also face internal discontent if their alliance partners are perceived to be prioritising some of their interests over others. For example, some members of NATO have argued that their contributions to the alliance’s mission in Afghanistan are being devalued because of the focus on counterterrorism over other priorities such as development and women’s rights.