King Xerxes’ huge Persian force of 250,000 sailors and soldiers could not defeat a rather poor Greece in 480 b.c. Yet a century and a half later, a much smaller invading force from the north under Philip II of Macedon overwhelmed the far more prosperous Greek descendants of the victors of Salamis.
For hundreds of years, the outmanned legions of the tiny and poor Roman Republic survived foreign invasions. Yet centuries later, tribal Goths, Visigoths, Vandals, and Huns overran the huge Mediterranean-wide Roman Empire.
Read the rest of Victor Davis Hanson on the destruction of affluent societies.