Players that feel like they have no chance at winning may surrender out of a game by clicking the Menu button in the lower-left, then Surrender.
It's Important to remember to keep playing until the surrender is accepted unless Instant Surrender is turned on.
 Instant Surrender
Game creators can decide whether surrenders happen instantly or require that all other active players in the game accept the surrender. The default is for surrenders to require acceptance.
 Surrender into AIs
Game creators can decide whether surrendered players are replaced by an AI or not. When disabled, surrendered player's territories and armies will turn into neutrals. If enabled, the player will be replaced with an AI, which will continue to operate their empire for them.