I sometimes think of game theory as being roughly divided in three parts, like Gaul. There's competitive zero-sum game theory, there's cooperative game theory, and there are games where players compete but also have some shared interest

Almost all human interactions are the third type. In fact, I think of this not as 3 parts, but as one thing - strategy, which has (at least) 2 special cases that have been studied: zero-sum and cooperative positive-sum. These special cases are interesting not because they occur, but because they illuminate aspects of the whole.