My enemy's enemy
“”The enemy of my enemy dies next.
"My enemy's enemy is my friend" is an old Arab saying. It explains some strange political, religious and epistemological alliances, such as the Second World War alliance of the US and Britain with the USSR, the alliance between the US and Pol Pot, or the Mormons and Catholics during the Proposition 8 campaign in California.
A short-hand version of the saying provides the name for this proverb's entry on Tv Tropes Wiki, where it's known as "Enemy Mine" not to be confused with the film starring Dennis Quaid or the story by Barry Longyear.
The Communist Party of Great Britain (Marxist-Leninist) uses this argument extensively in international relations.