The Domino effect --- It is similar to the Slippery Slope: Once something is allowed to happen (or provoked) it will cascade a sequential succession of deads in an irremediable fashion.

(It was the logic behind the U.S. intervention in the Korean and Vietnam wars: to stop the cascading spread of communism by China that supposedly would have taken place if those two nations were left to their own devices in their corresponding civil wars).

Source author: Eric Suzán Reed esuzan@sre.gob.mx