Why do we fight wars?

Once upon a time wars were fought for profit; when Rome established its empire or Spain conquered Peru, it was all about the land, the gold and silver, the slaves.
And that kind of thing still happens.
Or at least that is the official reason to wage a war, even though more than gold the goal is natural resources, oil, gas, land.
However, war — even easy, victorious war — doesn’t pay.
And this has been true for a long time.
War would necessarily inflict severe economic harm even on the victor.
Furthermore, it’s very hard to extract golden eggs from sophisticated economies without killing the goose in the process.

Besides, modern war is very, very expensive.
For example, by any estimate the eventual costs (including things like veterans’ care) of the Iraq war will end up being well over $1 trillion, that is, many times Iraq’s entire G.D.P.
So, if modern nations can’t enrich themselves by waging war and wars keep happening, one asks: why?
One answer could be that leaders do not understand the arithmetic.
My answer is that they do understand arithmetic, but do not follow the will of their people.
They do not wage wars in the interest of the people, or the nation.
As everything they do, is NOT what the citizens want, but WHAT the people who put them there want.
A country like US, where the economy is based on the production of weapons, HAS to wage wars, in order to produce more and more.
And it doesn´t matter how much they cost, or which profit they produce.
The profit is in the production and sale of weapons.
Governments too often gain politically from war, even if the war in question makes no sense in terms of national interests.