They don't think it bestows any glory, and they only go to war to protect their own land, their friend's land, or to free people being oppressed.
For example, when Hythloday's ship was there, they fought a war on behalf of the Nephelogetes against the Alaopolitans since the A Nephelogetes had been wronged.
In general, the Utopians react much more harshly to harm done to their friends than to harm done to themselves. Talk about selflessness.
They don't celebrate their accomplishments in war because they think don't consider them particularly impressive. They never try to win more than they had before the war started, only to return everything to the way it was.
Once war begins, they send in secret agents who try to execute the big officials before any fighting starts; they either do it themselves or try to turn their own people against them. This way, those actually in power are punished, and innocent lives lost in fighting can be spared.
They'll also try to stir up conflict within the enemy's own forces to make them less unified.
When they offer to help another nation, they are very generous with money, but not with soldiers.
In general, they prefer to hire other people to fight for them, especially a neighboring people called the Zapoletes. These guys are rough, mountain-dwellers and, if the price is right, they fight loyally for anyone who needs them. They love money so much that they will engage in the most intense and dangerous fighting if the price is right.
Utopia contributes its own men to fight only as a last resort, and when they do, their wives are allowed to go with them to make the whole thing easier.
Even though Utopians don't like to fight, when they do, they're awesome: brave and devoted.
Once they win, they certainly don't massacre the enemy, but instead take prisoners.
They are very sneaky about ambushing the enemy, and pretty great at avoiding ambushes themselves.
Because they're all completely willing to work together, fighting and defending goes quickly and efficiently.
They have great armor that both protects and easily allows for moving around—even swimming!
If there is a truce, the Utopians take it very seriously and don't ruin enemy land or people. They do collect a certain amount of money and land to make up for what the war cost them.
If another nation tries to invade Utopia, they immediately stop them and never let another army set foot on their island.