Goa, May 16 -- As global attention remained fixed on wars in the Middle East, rising tensions in the Taiwan Strait, and the increasingly fragile relationship between Washington and Beijing, many expected this week's meeting between Xi Jinping and Donald Trump to revolve around trade, military competition, and regional security.

Instead, Xi Jinping reached back more than two thousand years into ancient Greek history to frame one of the most important geopolitical questions of the modern era.

During his opening remarks in Beijing, the Chinese president invoked the Peloponnesian War - the devastating conflict fought between Athens and Sparta beginning in 431 BC. In doing so, Xi referenced what has become one of the most debated theories in...