First of all, other people are not used to playing this game. You are competing with robots. This entails a fight to the death between you and a group of AI.
You are placed into a game that is already in progress, thus some bots may already have taken over part of the arena. The game also includes new bot additions. In other words, they won't stop coming no matter how many bots you kill. You can only count on one feature of their spawning: they will never spawn in your own region. The number of bots in relation to the amount of land you have conquered is directly related to how challenging the game is.