Romulans would be ruthless!
moving in quickly like Mongul hoards and securing worlds for their own ends; sweeping expanse into what is (or would have been) Federation space
Klingons would be like the Philistines of the Old Testement after the Egyptian expanse-
"hiring themselves out" in exchange for the means to regain their might and retain their independance
No quarter with the Federation, it's their fault, them and thier Vulcan thinkers...!