You're right, of course. But military buildup has its limits, anyways. As an economy, you just can't go round the world for a long/sustainable time printing money, developing, building and stockpiling armament, and destroying all and everyone that doesn't want to abide to your rules/use your coins. Indeed, that's what's happening in the Iranian case actually. They just can't go and destroy Iran, because the consequences and complications of doing that are bigger than the fact that the Iranians are not using exclusively dollars anymore to sell their oil. Think about the costs, both in economic and human terms. The Iraq war, by example, had a cost in human lives bigger than a million people. And those costs are not only external, but also internal. You need to exert more and more pressure over time on your own and allied countries's populace to have enough soldiers (and supporters), willing to believe, to fight and to die to sustain your empire.
That doesn't mean that they won't try it anyways. But technically, that will only accelerate the empire's collapse/implosion. And the other technical problem is that, although you do that to sustain your currency, anyways you've printed a lot of it already, to sustain your empire. There are simply not enough goods and services to redeem so much printed green paper, so the printed green paper devaluates. And when that starts to happen, it can happen very fast. This is a problem, in fact, with all kinds of debt-based(interest yields) currencies. The illusion of endless growth reveals itself as what really is. Technically in these cases, the economy return to the fundamentals(that are not bad, certainly) very quickly also. Mauro Taylor J. Smith wrote:
