Ancient farming communities suffered violent attacks by nomads on horsebacks before technologies spread to help them become more warlike, according to new research.
Researchers at the University of Exeter discovered that war has been the "driving force" which has created the societies we live in today.
The academics, along with colleagues at the University of Connecticut, found that small, tightknit groups evolved into ancient empires as a result of large-scale, intense warfare.
"War was indeed a disruptive innovation which greatly accelerated the evolution of social complexity," said study author Professor Sergey Gavrilets of the University of Tennesee-Knoxville in America.
The researchers developed a mathematical model that can predict with 65% accuracy where and when the largest complex societies arose in human history. They used a computer simulation to show how war and ideas "spread" across the world over 3,000 years.
"The story of our past is not just a case of 'one damned thing after another," wrote lead author Peter Turchin, a University of Connecticut professor. "There are general mechanisms at play in shaping the broad patterns of history."
Their study concluded that an increase in the intensity of armed combat, and the spread of military technology, spurred the rise of vast, organised states. Dr Tom Currie from the University of Exeter, said: "The study helps us understand what forces favour the development of cultural traits that help keep large societies bonded together, and may help explain some of the inequalities we see in the world today."
The landscape was divided into grid cells characterised by elevation, whether or not the region had agriculture, and the type of habitat – grassland or desert.
The researchers used mathematical formulas to simulate warfare between societies, the spread of military technology, and socio-cultural evolution.
The model was tested against the historical record of empire formation in Europe, Africa and Asia during 1500 BC – 1500 AD, during which horse-related military innovations, including chariots and cavalry, dominated warfare across many regions.
Forces of warriors on horseback allowed large, powerful societies to flourish – by eliminating the weak, and spreading technologies which allowed more war, the researchers found.
Conquered societies would also tend to adopt traits such as religion, education and a bureaucratic class from their conquerors – as well as learning their military techniques.
Prof Gavrilets, said: "What's so exciting about this area of research is that instead of just telling stories or describing what occurred, we can now explain general historical patterns with quantitative accuracy. Explaining historical events helps us better understand the present, and ultimately may help us predict the future."