The phrase the enemy of my enemy is my friend is a proverb that advances the concept that because two parties have a common enemy, they can work with each other to advance their common goals. Often described as an Arabic proverb, there is also an identical Chinese proverb.

In foreign policy, it’s a doctrine commonly used to interact with a significant enemy through an intermediary rather than through direct confrontation.

Examples throughout history are common, such as longtime enemies Britain and France uniting against Germany during World War I, the Western capitalist democracies aiding the Soviet Union following the Nazi invasion during World War II, or U.S. support for anti-Communist dictatorships during the Cold War.

Using a common enemy as the basis for an allegiance is problematic unless there are other substantial areas for common ground, otherwise absent the common enemy the friends might well be enemies themselves. If the common enemy disappears, the allies might turn on each other. This has been shown before, such as at the end of World War II; without a common enemy, the differences between the United States, the United Kingdom and France and their Soviet allies were no longer accepted because the threat they shared was absent. Cartoonist Howard Tayler, using humor toward social critique, condenses the concept into ‘Maxim 29’, “The enemy of my enemy is my enemy’s enemy. No more. No less.”

Sometimes two hostile parties may remain hostile even in the face of a third party hostile to both for example, in the opening stages of the portions of the Bosnian War of the 1990s could be described as a “three-cornered” conflict with Croat, Bosniak and Serb forces all fighting one another. In extremely rare cases, a conflict might be between four parties or more.

On the other hand, if parties that share common ground in other areas later find the need to ally against a common enemy, the ensuing alliance might endure even after the threat disappears such examples might be the states that formed the USA.