 Amazingly, the Persians who until that time had enjoyed a largely unchallenged dominance over the region put up little resistance.Alexander left trusted lieutenants as well as former Persian satraps to rule his new conquests as he continued on his relentless thrust to the very edge of the known world.Alexander's conquest of Persia replaced the Achaemenids with the Seleucids, but the absence of a clear successor after his untimely death and the in-fighting that inevitably followed, meant that his empire would not long outlive him.