From 9/11's ashes, a new world took shape. It did not last.

In the ghastly rubble of ground zero’s fallen towers 20 years ago, Hour Zero arrived, a chance to start anew.

World affairs reordered abruptly on that morning of blue skies, black ash, fire and death.

In Iran, chants of “death to America” quickly gave way to candlelight vigils to mourn the American dead. Vladimir Putin weighed in with substantive help as the U.S. prepared to go to war in Russia’s region of influence.

Libya’s Moammar Gadhafi, a murderous dictator with a poetic streak, spoke of the “human duty” to be...