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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 US prepared to go to war in Russia's region of influence.
Libya's Muammar Gaddafi, a murderous dictator with a poetic streak, spoke of the "human duty" to be with Americans after "these horrifying and awesome events, which are bound to awaken human conscience".
From the first terrible moments, America's longstanding allies were joined by longtime enemies in that galvanising instant. No nation with global standing was cheering the stateless terrorists. How rare is that?
Too rare to last, it turned out.
Civilisations have their allegories for rebirth in times of devastation. A global favourite is the phoenix rising from ashes. In the hellscape of Germany at the end of World War II, the concept of Hour Zero, or Stunde Null, offered the opportunity to start anew.
For the US, September 11, 2001, meant a chance to reshape its place in the post-Cold War world from a high perch of influence and goodwill. This was only a decade after the Soviet Union's collapse left America with both the moral authority and the muscle to be the lone superpower.
Those advantages were soon squandered. Instead of a new order, 9/11 fuelled 20 years of war abroad. In the US, it gave rise to the angry, aggrieved, self-proclaimed patriot, and heightened surveillance and suspicion in the name of common defence.
It opened an era of deference to the armed forces as lawmakers pulled back on oversight as presidents gave primacy to the military over law enforcement in counterterrorism. It sparked anti-immigrant sentiment, primarily directed at Muslim countries, that lingers today.
What most nations agreed was a war of necessity in Afghanistan was followed two years later by a war of choice as the US invaded Iraq on false claims that Saddam Hussein was hiding weapons of mass destruction.
Thus began the notion of "forever wars". Convulsions ran through the Middle East and steady US foreign policy gave way to a sudden changes from Bush to Obama to Trump. Trust in America's leadership and reliability waned.
Other parts of the world were not immune. Far-right populist movements coursed through Europe. Britain voted to break away from the European Union. China steadily ascended in the global pecking order.
Now, President Joe Biden is trying to restore trust, but there is no easy path.
In Afghanistan in August, the Taliban swiftly seized control as Afghan government forces the US and its allies had spent two decades trying to build collapsed. No steady hand was evident from the US in the disorganised evacuation of Afghans trying to flee the country.
In the US, the 2001 attacks set loose a cry for revenge. A swath of American society embraced Bush's outlook - "Either you are with us, or you are with the terrorists" - and hasn't let go of it.
Factionalism hardened. The concept of enemy evolved to include immigrants as well as terrorists.
The patriot under threat became a personal and political identity. Trump would harness it to help him win the presidency.
For the US, the presidencies since Bush's wars have been marked by an effort to pull back the military from the conflicts of the Middle East and Central Asia.
The perception of a US retreat allowed Russia and China to gain influence in the regions and left US allies struggling to understand Washington's place in the world. The notion that 9/11 would create an enduring unity of interest to combat terrorism collided with rising nationalism and a US president, Trump, who disdained the NATO allies that in 2001 had rallied to America's cause.
To be sure, US presidents since 9/11 have shored up security, and US territory has remained safe from more international terrorism near the scale of 9/11.
Globally, US-led forces weakened al-Qaeda, which has failed to launch a major attack on the West since 2005. The Iraq invasion rid the world of a murderous dictator in Saddam.
Yet deadly chaos soon followed his overthrow. The Bush administration failed to plan for keeping order, leaving Islamist extremists and rival militias to fight for dominance.
Today, the legacies of 9/11 ripple both in different ways.
Most directly, millions of people in the US and Europe go about their public business under the gaze of security cameras, while other surveillance tools scoop up private communications. The government layered post-9/11 bureaucracies on to law enforcement to support the expansive security apparatus. Government offices became fortifications; airports a security maze.
But 9/11's effect on how the world has been ordered was temporary and largely undone by domestic political forces, a global economic downturn and now a lethal pandemic.
The awakening of human conscience predicted by Gaddafi didn't last. Gaddafi didn't last.
Osama bin Laden has been dead for a decade. Saddam was hanged in 2006. The forever wars are over or ending. The days of Russia tactically enabling the US, and China not standing in the way, petered out.
Only the phoenix lasts.