The opening scene in the story I'm currently working on is an interplanetary invasion. Writing this scene has troubled me not because it is a sweeping vista of giant ships, a city under attack and troop movements but because of economics.
The Stainless Steel Rat stories by Harry Harrison formed a large part of my early SF education. I can still remember the thrill of reading the first page of the original book and I steadily worked my way through them all. The Deathword series were faves too. Jim De Griz! Jason Dinalt!
Woah, just found out Slippery Jim originated in a short story in August 1957 in Astounding.
One section in The Stainless Steel Rat's Revenge really stuck with me. It was a passage about the economics of interstellar war. It's ruinously expensive so pretty much no-one will bother in the far future, suggested Mr Harrison. That bugged me then and it bugs me now. I remember wondering if that would be the case. That, when war is too expensive, nations will not bother. Really? Really?
Lots has been written about the economics of post-scarcity societies. Some of it by economists and some by science fiction writers. Astonishingly, Nobel laureate Paul Krugman became an economist because it was the closest thing he could find to being a psychohistorian.
Anyhoo, having read a few of the pieces gathered here, here and here none have put a price on whether it is economically feasible. It's true at the moment that war is costly but we are in a scarcity society and are subject to the laws of supply and demand.
Post-scarcity opens up lots more options i.e. hand waving. Given fewer restrictions on materials and far lower costs of production then it may be more feasible. It's never going to be free and it does assume a vigorous and sustained military organisation to provide the bodies and fight the battles. Maybe that's the bigger problem. That its plausibility assumes a society happy to have a lot of its productive people locked away and prepared to fight. If the AIs are in charge would they be happy to do that. What if they are forced to? Hmmm. Maybe it will work, if only because the backdrop informs the story.