In days of yore, men submitted to whichever member of the tribe was the mightiest in battle. By doing so, they stood a better chance of succeeding in battle, thereby diminishing the likelihood of their own death or enslavement.
Later on, as tribes became more tied to the land and communities sprang up, the idea of a strong leader still made sense. Not only might he do the best job of leading the protection of the town or village, he might also travel outside the community to attack other communities, bringing back spoils for all to benefit from. (Not too civilised, maybe, but still, the reasoning behind submission to the leader made sense.)
Later, settlements grew larger and, increasingly, many villages and towns would find themselves joined together collectively, under a national banner, with a single army to protect them. And, again, the leader would most likely be a fierce and formidable warrior.