This article is a general, nonpartisan explainer. It describes the United States unless stated otherwise, and details change over time, so check official sources for the latest.
States form alliances to improve their security by pooling resources, sharing information, and signaling resolve. The best known today is the North Atlantic Treaty Organization, but there are many bilateral and regional arrangements.
Why states ally
- To deter a common threat.
- To share the cost of defense.
- To gain access to bases, intelligence, and markets.
- To influence the behavior of partners.
Burden-sharing
Burden-sharing refers to how fairly the costs and risks of an alliance are divided. Contributions can be measured by defense spending, troops, bases, or political support. Large members often argue that smaller ones should contribute more, while smaller ones point to other kinds of contributions.
In 2014, NATO members pledged to move toward spending two percent of their gross domestic product on defense within a decade. More recent commitments have set higher targets, so check current NATO documents for the latest.
Trade-offs
- Abandonment: the fear that an ally will not come to your defense.
- Entrapment: the fear of being pulled into a conflict by an ally’s actions.
- Free riding: relying on others to pay.
Beyond spending
Spending figures do not tell the whole story. Capabilities, interoperability, readiness, and willingness to deploy forces matter as well. Allies also contribute by hosting bases or providing diplomatic backing.
Keeping alliances healthy
Regular consultation, joint exercises, and clear political commitments help to maintain trust. Disagreements are normal in alliances, particularly among democracies, and are usually negotiated rather than resolved by one side alone.
Understanding alliances means looking at both what members promise and what they actually do.
