If anything, it is politicians who determine the economic policy of a country and ultimately its fate, not economists. Politics has the upper hand in the economic matters, and to prove that is in fact pretty easy. Most wars turn out an economic disaster for the belligerent countries (it has been so for millenia), while the questions of peace and war are in the hands of a few people who may not have a damn clue about economics and how the economy works. In other words, it remains to be seen whether political decisions are actually aimed at strengthening the economic conditions of a country as it may well be to the contrary
Could those people actually end up having economic benefits from wars? Direct of indirect benefits?
This is certainly possible
Ultimately, it all depends on how successful these people are at warfare and ensuing dominion (remember, the winner takes it all, the loser's standing small). The most conspicuous example of this kind is the Roman Empire (first Republic, or how it was called before it became an empire). It led quite a number of successful wars through which it expanded its territory manifold and promoted economic wellbeing of its citizens
And when it finally collapsed, it was mostly due to internal corruption and discord, not wars of conquest as such. As a matter of fact, the Roman Empire even began to shrink near the end of its rule as it was no longer able to protect its lengthy borders due to continual economic and political failure of the state (e.g. Romans withdrew from Britain in the late 4th century about a hundred years prior to the fall of Rome herself)
Centralization of power and situation where economic operators are dependent on government to operate creates situations of monopolies, corruption, etc...
Well, technically, centralization of power doesn't necessarily mean centralization of economy through monopolies, etc. Although such centralization definitely creates certain incentives, you may still have a kind of monarchy with a properly decentralized economy