How does Gulliver justify the different reasons why one country wages war against another and justifies it even when according to all rules of justice it is wrong? Elaborate.

Basically Gulliver explains that war is justified for reasons of  greed, power, superiority, and the violence of human nature. Of course the Houyhnhnms find all these traits offensive. 

“Sometimes the quarrel between two princes is to decide which of them shall dispossess a third of his dominions, where neither of them pretend to any right. Sometimes one prince quarrels with another for fear the other should quarrel with him. Sometimes a war is entered upon, because the enemy is too strong; and sometimes, because he is too weak. Sometimes our neighbours want the things which we have, or have the things which we want, and we both fight, till they take ours, or give us theirs. It is a very justifiable cause of a war, to invade a country after the people have been wasted by famine, destroyed by pestilence, or embroiled by factions among themselves. It is justifiable to enter into war against our nearest ally, when one of his towns lies convenient for us, or a territory of land, that would render our dominions round and complete." Ch 5