factions joining forces against a common enemy theme

also known as: the enemy of my enemy is my friend

Two sovereign factions put their differences aside and make common cause for the purpose of opposing a third faction.

Examples

Captain Kirk's crew and the Klingons joined forces against a mysterious cloud being in tos3x11 "Day of the Dove".

35 total · 9 choice · 15 major · 11 minor

StoryLevelMotivation
bbf3x15 choice Sheridan tried to organize resistance
bbf4x11 choice Franklin forged alliance on Mars, Delenn failed to forge with aliens
ds95x15 choice Federation and Romulan and Klingon Empires unite to thwart Dominion invasion of the Alpha Quadrant; prisoners from hostile alien races join forces to escape
got7x05 choice Jon wanted from Daenerys and now potentially Cerci
got7x07 choice Jon wanted from Daenerys and now potentially Cerci
ldr2019e4x04 choice The rival gangs teamed up to battle the baby-shaped gargantuans that were ravaging the city.
movie: Independence Day (1996) choice The film pointedly culminates with the countries of the world joining forces to defeat a seemingly invincible alien armada that was hellbent on exterminating the human race.
voy3x26 choice The Voyager crew made a reluctant alliance with humankind's mortal enemy the Borg to fight their common enemy: Species 8472.
voy4x01 choice The Voyager crew made a reluctant alliance with humankind's mortal enemy the Borg to fight their common enemy: Species 8472.
bbf4x01 major the alliance against the shadows was fracturing