Empire inherently requires a debasement of the currency, and in the case of a fiat paper money system, it can lead to hyperinflation. You mentioned the cutting of social programs in order to pay for the empire, but that won't happen in the US. Our government will opt for inflation every time. As long as the printing press is running, there will be money to pay for perpetual war, as well as socialist spending programs on the domestic front. The thing is, once the citizenry gets a clue and finally realizes what is going on, I think some sort of revolution will occur, and the printing press will be destroyed.
I realize reality is different than the hypotheticals I keep proposing, but they’re just that: hypotheticals. In reality of course empires have proven to be unsustainable. History provides many examples of this. As far as social programs being cut, it saddens me to admit that you are right and that people rarely give up their handout.
It’ll definitely be interesting to see how events unfold in the next few decades.