Unending war for inchoate purposes at the behest of an amoral system will sap morale.
“When you engage in actual fighting, if victory is long in coming, then men’s weapons will grow dull and their ardor will be damped. If you lay siege to a town, you will exhaust your strength.
Again, if the campaign is protracted, the resources of the State will not be equal to the strain.
Now, when your weapons are dulled, your ardor damped, your strength exhausted and your treasure spent, other chieftains will spring up to take advantage of your extremity. Then no man, however wise, will be able to avert the consequences that must ensue.”
- Sun Tzu
Quite up to date.