Great Greek historian and general Thucydides, writing in 5th Century BC, devised the most insightful theory of international relations. It is a theory that is as relevant today, two-and-a-half millennia later, than it was at the time of writing.
Known as the Thucydides trap, and based on his analysis of the Peloponnesian War between the city states of Sparta and Athens, the theory explains that when a rising power challenges an existing power’s dominance, the older force is likely to respond with violence, ultimately resulting in war between the old and the new.