That's what it's good for
War is one of the biggest differences between 7 Wonders and Duel. War cards now push the Conflict marker along its track and one player gains points from its position at the end of the game.
But if you manage to push the marker all the way to your opponents capital, then the game ends immediately and you win.
(The metal conflict marker is plastic as a standard components, metal was an Essen extra)