A historian's read on empire decline says a U.S. war with Iran would turn into a losing quagmire — bad news for anyone expecting a quick American victory.

• The core claim: empires in decline start wars they think are easy, and Iran would be that war for the U.S.
• The driver is hubris — believing you cannot be touched, so you pick fights that drain you.
• The pattern goes back a long way: Persia's invasion of Greece, Athens' disastrous attack on Sicily, and Vietnam more recently.
• The practical problem is capacity — the U.S. lacks the factories and supply lines to sustain a long fight in Iran's mountains.

Outlook: If Washington escalates with Iran, expect a drawn-out conflict rather than a fast win.