The Enemy of my Enemy is my Friend: the Structural Balance Property in International Relations
There is an old saying “the enemy of my enemy is my friend.” This is taken to be common sense. Two countries which have negative relations with a third country can work together to ensure that their mutual enemy does not become too powerful. This is one of the examples of the Structural Balance Property. This property states that in any three way relationship, the relationship is stable if there exists either one positive tie or three positive ties. This means that either two entities are on good terms and they are enemies with a third entity, or all three entities have friendly relations. Balance in this context means that the network will not change. Unbalanced networks consist of all three parties hating each other(in this case the weaker two will team up against the stronger player) or a player having strong relations with two players who hate each other(in this case the one who is friends with the two players that hate each other will eventually grow to hate one of his/her friends).
The scenario that I described initially, in which two parties team up against a mutual enemy explains why seemingly disparate groups can be seen working together in many instances. This happens all the time in politics. In countries which have more than two political parties, this is known as a coalition. This also occurs on the international level. Countries often work together to curb the interests of their mutual enemies. One such instance of this in the world today is a quasi–alliance known as the Quadrilateral Security Dialogue, colloquially referred to as the Quad. The Quad consists of the United States, Australia, Japan, and India. The Quad’s aim is to ensure that China, a common enemy of each member, doesn’t grow too powerful. This effort to restrain China explains why these four countries are working together.
Sources:
https://www.journals.uchicago.edu/doi/10.1111/j.1468-2508.2007.00497.x