When different groups of people or countries fight each other, they may take things from each other as a reward for their victory. These things can include other people, animals, valuables like gold or silver, or even pieces of land. This is what is called the "prize of war". It is like a big game, except very serious and not fun at all. Winning this "game" means getting things that you did not have before, but it often comes at a high cost, as people may be hurt or killed in the process. In the end, the "prize of war" is really just a fancy way of saying that one group managed to take things from another group by force, which is never a good thing.