Wars in reality are generally unpleasant affairs. When it comes to fiction, however, wars are immensely useful. Their great versatility in worldbuilding inspired me to call them the Swiss army knife of worldbuilding tools, which is probably dumb but I'm sticking to it. People like to use sayings such as “violence doesn't solve anything” and “fighting is never the answer,” but those people are dead wrong when it comes to worldbuilding. Wars are so great for shaping a fictional world that using them almost feels like cheating, just a short step down from a straight up deus ex machina, but instead of being nonsense pulled out of nowhere they actually add depth to your world. That's enough generic hyping of the topic, I suppose. I'll provide a bunch of examples to show you what I mean, but they will by no means be comprehensive. Wars can be used for so many purposes in worldbuilding that trying to nail down every little facet would require at least a short novel worth of text. Never underestimate the transformative power of thousands of people being angry or stupid enough to kill each other en masse. Culture Wars have the potential to alter pretty much anything about the culture of a participating nation. Generally speaking, if you want a culture to undergo some kind of change but aren't sure how to get from point A to point B, then you can probably solve the dilemma with a war. Maybe you want one or more leader type people to be replaced by someone else. Maybe you want the form of government to change entirely. Maybe you want some political faction to take over where another one ruled, but a normal election type thing is too boring for you. You can make these political changes and more through the expedient of a civil war. Wars can lead to social upheaval in more subtle ways as well. People could start to dislike their ruler and get all sorts of rebellious during/after a very costly war, especially if there wasn't sufficient propaganda spread around to convince people it was necessary. Values and morality standards can change a lot depending on the outcome of a war and what sort of stories came back from it. Honestly, I can't think of a single kind of social paradigm shift that couldn't be attributed to a war. You can use wars to create anything from an amicable rivalry to disdain to outright prejudice between two nations and their people. Two nations that compete for dominance in a region of the world without much fighting with each other, perhaps even aiding one another in dealing with others who start trouble in their neighborhood, could grow to be pals whose people make well meaning jokes about which county is better. Two nations with a history of warring with one another, even if it's a long time past, may end up disliking one another, and as such their people would make more spiteful remarks about each other. If you have one nation just completely wreck another, especially if they occupy the place and be real assholes about the whole thing, odds are good you're gonna get some prejudice going on both ways: the victors will see the losers as lesser people, and the losers will see the victors as monstrous oppressors. Wars can also do crazy things to a nation's economy. A war can be used to make a nation wealthy or to leave it destitute: just have them win for riches or lose to become poor. You can also get more specific with bits of the economy if you feel like it. For instance, if you want a nation to be the main supplier of weapons or armor or warships or other costly war things for other nations, then give them a history of participating in wars so that having that kind of production infrastructure in place makes sense. Losing a war and becoming occupied for a long time could lead to a nation being stripped of most of its natural resources, leaving it unable to produce much in the way of weapons or luxury goods. If you want a culture to be generally peaceful, giving them a history of losing in wars is a decent way to have that make sense; after enough times of getting the crap kicked out of them, pretty much anyone would just want it to stop. On the flip side, a history of successful warring could make for a very aggressive populace. You can also causes these sorts of attitudes without direct war participation: people in regions of the world where there have been no wars for a long time may become complacent and peaceful, where as people in regions with a lot of war may become warlike themselves. You can make a particular place in your world become very diverse in nationalities or races or whatever by having a lot of nearby nations get into a big war that the burgeoning land of diversity stays out of, thus becoming a bastion for refugees. This could either turn it into a sort of melting pot situation where folks are more tolerant of one another, or it could become incredibly tense with lots of assaults and fights and stuff going on between people from nations on different sides of the war. Religions can rise or fall in power and influence by way of their interaction with war. If they support a side that ends up winning, odds are good they'll become more powerful and influential in that nation due to that support. If they instead support a loser, they won't have much to gain from a beaten nation and might also become reviled by those who were on the winning team. Various arts in all mediums could see a surge in creation due to war. Perhaps a painter will romanticize the whole thing and create stirring and patriotic images, maybe a musician will be saddened by all the loss of life and write sorrowful tunes to express it, so on and so forth. Folk heroes are a nice little way to flesh out a culture, and folk heroes tend to be created during wars. They might be actual soldiers who did great things and then had people create a whole mythos around them to boost morale, or they might be entirely fictional creations that do the same thing. Science, Technology, and Magic Wars have spurred discovery and innovation for the entire history of humanity. There is no reason this shouldn't also be the case in fiction. Weapons are, of course, the obvious thing one would expect to be made during a war. Better swords, bigger guns, scarier magic spells, anything to kill the enemy harder and faster than they can kill your guys. If you need to explain the creation of some kind of weapon you plain old made up, or that is more advanced than the setting might seem to call for, then wartime innovation is a good answer. Defensive measures are also pretty standard for war inventions. Techniques to make higher quality armor, methods to counter new enemy weapons, figuring out ways to hide your important stuff from the enemy, and so on. Same as the above: if you need to explain something that's new or anachronistic, say it was made because of a war. Communication is rather important for war, so any advances in that area can be attributed to war necessity as well. Let's say your world has some genetically engineered telepathic people that can just communicate mentally over long distances. It would make sense for them to be created in war time, perhaps while in pursuit of making some sort of super soldier. Getting things from one place to another is also pretty vital for war. New forms of transportation and improvements on old ones could all come from war innovation. If you've got magic in your world, teleporting things might have been made possible by someone researching a way to get supplies to soldiers without needing pesky supply routes and such. All sorts of useful medical inventions and techniques crop up during war, for rather obvious reasons. When you've got thousands of people dying, doctors will look for quicker and better ways to deal with problems, and that leads to invention. Items of practical convenience also tend to come into prominence during wars. For instance, the wristwatch first became a big thing in World War I due to them being so useful for timing artillery barrages with infantry advances. The zipper replaced clasps and hooks for a lot of clothing because the US military incorporated them into uniforms. Pretty much anything that saves time and is convenient and could make sense to have some kind of military application could be attributed to wartime innovation. Accidental discoveries and finding new uses for existing inventions are also a regular thing during wars. My favorite example of this is how tampons were originally made to plug up bullet wounds, but then someone realized they could be used in another way. This lovely little catch all means that anything that could be reasonably finagled into being accidentally discovered in the process of trying to make things for war can easily be claimed as a wartime creation. Other Wars make great basic building blocks for your world history. Aside from being able to do everything else listed in this workshop, historical wars can act as period and era markers for your world. You could make a reasonably comprehensive history of Europe as a whole just by listing off all the wars and giving a paragraph or two of contextual information for each one, and the same can be done with your created world if you use them liberally enough. Wars also make great space fillers. If you create a timeline for your world and notice a large gap with nothing interesting going on, screw it, throw in a war. No need to shoehorn something in that ties in with the main plot, just throw a few thousand nameless historical soldiers at each other and reduce it to a simple line telling the names of the participants and who won. Wanna have a major change in national borders, or the complete eradication of a nation, or even the creation of a completely new nation? War is the most logical possible cause for such things. You can also use war as a good background for the current plot of your story, whatever it is. Whether it's a recently finished war, a war in progress, or a war on the horizon, the drama and tension involved can make for some fun events. Wars in the past can also work as justification for conflict in the present. Want to have two nations at war but you can't think of a good reason? Give them a history of going to war with each other and hating each other, then all you need is some frivolous thing like a slightly important person getting killed by people of the enemy country to act as the spark in the powder keg. A long history of war and enmity between two nations can also act as explanation for smaller fights of one side versus another, anything from a random battle between two regiments of soldiers to a bar fight to a one on one knife fight. Conclusion All the above ideas were the product of less than half an hour of brainstorming. There are probably some obvious things that I missed, but that's fine. I think this should be enough war advocacy to get my point across about how versatile wars can be for worldbuilders. Now that you've read through this, hopefully you'll make use of this grand tool more often. Go on, get out there and start some fictional wars to improve your fictional worlds. Oh, also, feel free to respond with further examples of how wars can work as worldbuilding tools if you like. The more the merrier, as the saying goes.