It’s vaguely referenced in The Last Jedi, but it doesn’t really go anywhere. Finn discovers the dude they stole the ship from was selling military hardware to both sides, and that’s basically all it ever comes up.

It is more of a big theme in the prequels, where you have the constant undercurrent of Palpatine orchestrating the conflict and driving the war machine for both sides. It comes up a lot in the Clone Wars show. But even then it’s not really about both sides driving perpetual war so much as how he used civil unrest to justify a proxy war to solidify his own power.