It is a concept of Games theory . Games that involve more than two players are called N-person games . A complete analysis of such games is much more complex than zero-sum games.
Conflicts of interest are less obvious.
What is good for player 1 may be bad for player 2 but good for player 3. In such a situation coalitions may form and change a game radically. Would the weak gang up against the strong or would a weak player try to make an alliance with a strong one. Von Neumann hoped to use the minimax theorem to tackle games of even more players. He felt that a three person game could be looked at as two coalitions, and so effectively be a two person game with a solution guaranted by the minimax theorem.