In the realm of international relations, an alliance refers to a formal agreement between two or more states to provide mutual support in the event of a war. Modern alliances involve coordinated actions by independent states and primarily serve defensive purposes, requiring allies to come to each other’s aid if any member is attacked by another state or coalition. While alliances can be informal, they are typically established through a formal treaty that outlines the specific circumstances under which an ally is obligated to assist another member. These alliances emerge from the desire of states to maintain a balance of power among themselves.
In systems comprising several medium-sized countries, such as in Europe since the Middle Ages, no single state can establish long-term dominance over others, as remaining states form alliances to counterbalance any potential hegemony. This was evident in the opposition faced by King Louis XIV of France during his attempts to control continental Europe, resulting in a coalition known as the War of the Grand Alliance. Similarly, Napoleon’s ambitions were thwarted through the formation of alliances that united against him.