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"and what are the downsides"It works the same was in the US. Your taxes pay for the CIA, the CIA overthrows governments for United Fruit, and you buy products from United Fruit. You're paying for bananas twice and they are receiving "security" (wink, wink) for free[1]. Later, CIA high-ups get high-paid sinecures at the United Fruit company, making them the only ones getting compensated for the deployment of the government's resources. Russian citizens are not going to get parcels of land from occupied Ukraine. The soldiers who survive the war aren't going to get mineral rights. Instead of asking, "what are the downsides," a more pertinent question is, "who's getting the upsides?" (It is never you or me.) In practice, at least since the British Empire, wars of imperial expansion have served as another method of transferring resources from the public to a few influential business owners - corruption in so many words, not any different from stealing the funds for a highway.
In the middle ages and earlier, soldiers would be rewarded in the form of titles of nobility, or in the Roman Empire, with land and prisoners of war to use as slaves. If that was a practice anywhere in the world today, perhaps I'd comprehend the argument for war from the pursuit of economic interests. Then, at least, it would be a moral issue - otherwise, as it is today, it's another pretext for the few to steal from the many. That means you.
[1] https://en.wikipedia.org/wiki/1954_Guatemalan_coup_d%27%C3%A...