A long time ago in human history there were little tribes of people all around. One day a baby was born. This baby grew up to be hell bent on world domination. From some fluke of nature, this baby had an inkling to enjoy the idea of world domination. That's all it took. This baby then went on to rally his tribe to conquer a neighboring tribe. He then went on to conquer all the tribes in his known world. His genes that contained his love of world domination spread to his descendants. Like a tree branching out, his descendants branched out and conquered more and more all while spreading their genes.
Those tribes that lived in peace and harmony and thought that the world was a big enough place for all tribes were consumed by the tribes that contained leadership bent on world domination. When a dominating tribe met another dominating tribe, war also ensued. When both tribes were equally matched, boundaries were created. The dominating tribes would expand and consume until powerful opposition forced it to stop.
This consuming and expanding is what created the political boundary lines on maps in our atlases. Many countries would have gladly expanded into all of europe until it was one solid country. Opposing forces stopped this from occurring.
Our ancestry is full of conquerors. It is in our blood. Unless resistance is offered, conquerors will rise from our populations and try and follow through with their quest for domination. If you offer no resistance, you will be taken advantage of and consumed in an ever-expanding empire sought by a conqueror.