The Shia fault line: How a 1,400-year divide shapes the Iran crisis

From Egypt to Pakistan, the sectarian geography shows that US-Israeli strikes on Tehran are more than a bilateral conflict.

The United States and Israel struck Tehran and other Iranian cities Saturday, targeting a country that sits at the centre of Islam's oldest political fault line. Iran is 90 to 95 per cent Shia Muslim, the world's largest Shia-majority nation according to Pew Research Centre data, and the anchor of a sectarian geography stretching from the Mediterranean to the Hindu Kush.

That geography is now at the centre of a war.

Shia Muslims make up roughly 15 per cent of the world's Muslim population. The vast majority, about 85 per cent, are Sunni, according to Pew Research Centre estimates. But that minority is heavily concentrated in a corridor running from Lebanon through Iraq to Iran: the "Shia crescent," a term coined by Jordan's King Abdullah II in 2004.

Lebanon's Hezbollah is Shia, backed by Tehran. Iraq, by far the most populous Arab-majority Shia country in the world, with about two-thirds of its Muslim population identifying as Shia, maintains deep ties to Iran. Bahrain, where 65 to 75 per cent of Muslims are Shia, but the ruling monarchy is Sunni, has been a pressure point for decades.

Yemen's Houthi movement draws from the Zaidi Shia tradition, one reason Iran has backed it in the civil war. Shia make up 35 to 40 per cent of Yemen's Muslim population, concentrated in the north.

That network of Shia-majority or Shia-significant populations gives Iran reach far beyond its borders. A strike on Tehran is not a strike on one country. It is a strike at the centre of a transnational religious and political alliance.