Iran edges closer to a revolution that would reshape the world

As protesters pour into the streets of Iran night after night, leaders across the region and around the world are grappling with the possibility that the Islamic Republic could be overthrown — a seminal event that would transform global geopolitics and energy markets.

The regime of Supreme Leader Ayatollah Ali Khamenei has weathered bouts of protests many times, but demonstrations that began two weeks ago are spreading — by some accounts, hundreds of thousands of people defied authorities’...