end game

or endgame

noun

1. Chess. the final stage of a game, usually following the exchange of queens and the serious reduction of forces.
2. the late or final stages of any activity:

   the end game of the negotiations.

Word History and Origins

Origin of end game¹

First recorded in 1880–85

Idioms and Phrases

The final stage of some process, as in The book discussed the diplomatic end game resulting in the treaty . This term, dating from about 1880, comes from chess, where it denotes the stage of a game when most of the pieces have been removed from the board. In the mid-1900s it began to be transferred to other activities.