I am a military history buff. I was born right before the U.S. entered World War II. My uncle fought in both WWI and WWII. I was fascinated by pictures of airplanes and ships of war. When I learned to read I could happily settle down with a book such as "U.S. Destroyer Operations in WWII." The point is that I have been a student of the military and war for about 60 years. Without having served beyond R.O.T.C. in college (4-F) I have learned quite a lot about why wars are fought and how they are won.
One of the first things one learns about war is that it is expensive. Kings imposed taxes so they could conduct their wars. Nations go bankrupt attempting to pay for wars. Destruction of property is almost required when one conducts or even trains for war. The weapons of war are expensive. The distinction between a knight and a common foot-soldier was that the knight had an expensive horse and a fortune in armor and a sword which might have taken a man years to produce. Even just occupying a country that doesn’t want your army there costs a lot of money.
So why do nations/kingdoms/empires/city-states and such go to war? Because of the nature of their money, of course. Remember that a physical object money (POM) can be taken against the will of the owner. POM simulates a zero-sum game relationship, even among nations. POM can be used to motivate immoral behavior (such as hiring soldiers to invade a neighboring country).
Looking back over history, there has always been a monetary motive for every war. You can’t find a war that didn’t have someone on one side or the other expecting to gain financially from the war and usually both sides have that expectation. Those who provide the arms for a war know that there will be more business if there is a war. Those who serve in the army get paid and hope for loot. Those who work for the army bureaucracy get paid. The leaders/rulers can gain more territory to tax and loot. (Alexander the Great gained literally tons of gold and silver not to mention the gems.) Everywhere along the line people are hoping for and expecting to have the opportunity to gain wealth.
Usually it doesn’t work out to anyone’s benefit. Wars almost never go the way those who initiate them expect them to. Wars have large up-front costs and require considerable expenditures to keep going. But all along the way there is that temptation, that lure of the "big bucks," that keeps the leaders going. At least… they are kept going until survival and threats to life and limb provide motivation to change their minds.
From an historical perspective, it is obvious that war has been a singularly stupid human enterprise. Though there have been some benefits from war, overall the loss from war has been enormously greater in life, money and property. Yet, stupid and destructive as war has been for all the societies that have participated in warfare (and that includes almost all nations), war continues unabated around the world because the same kind of money, physical object money, is in use around the world in every nation.
The companion article to this article is "non-POM and War" which should be "nearby."