Ancient Assyria, the first regular army

If at the beginning of its history (2100 BC) the Assyrian empire only possessed an army of mere peasants pikemen, it quickly gained global supremacy in warfare thanks to two great innovations in weaponry : the use of the horse (war chariots) and of the iron (swords) combinated with a newly born administration (each warrior received a wage, specific buildings were created to store weapons, horses and food...). It gave to the Assyrian army two great advantages over the other powers (9th century BC) : a professionnal army (well trained, it would fight far better than levied peasants)  and in terms of technology (iron was more effective than bronze). This army relied upon a strong infantry as a backbone, and on chariots to protect its flanks. Very deadly in plain, it found itself also fairly good in uneven terrains (even if its chariots were uneffiicient in these conditions). More over, the Assyrians were fine siege crafters (they knew how to build towers, battering rams, engines able to throw burning materials on the walls...)