As a real world example, do some research on Ancient Greece during the Classical Period, where city-states such as Athens and Sparta would go to war all the time over something as simple as farmland for as little as a week.

The warlike culture in Ancient Greece was so ingrained in the people of their time that combat and war wasn't considered a matter of survival. It was a matter of pride and honor. I'm not saying they were a barbaric civilization or that everyone in Greece relished the bloodshed: Aristophanes' classic play "Lysistrata" (which was written near the end of the Peloponnesean War - again, I encourage you to look it up, as a dramaturge and historian I can say it's really exciting) shows that even a culture based on honor and pride could become war-weary.

Even in modern times, national military service is mandatory for all Israeli citizens over the age of 18: men serve three years in the Israeli Defense Force, while women serve two. Because of how ingrained it is in the culture, most of these young adults see it as an honor and their duty to protect their country from all the nations around it that are on really poor terms with Israel.

You don't have to understand it or even like it in comparison to today's society, but it's not as though there isn't any precedent in history for it.