(CNN) President Joe Biden's promise to remove US troops from Afghanistan by September 11 is his effort -- each of the last four presidents has had one -- to end America's longest war.
The deadline for Biden's withdrawal is significant -- September 11, 2021, is 20 years after the 9/11 terror attacks in New York, Washington, DC, and Pennsylvania that led the US to target Afghanistan in the first place.
Those two decades have seen more than 2,300 US military lives lost, tens of thousands of US wounded, countless Afghan casualties and more than $2 trillion in taxpayer money spent.
After all that, the last US troops to depart -- some of them surely born after the 9/11 attacks -- will leave parts of Afghanistan under the control of the same oppressive Taliban leaders who were there in 2001.
Here is a brief attempt to bring those 20 years of war into perspective.
The Soviets occupied Afghanistan during the 1980s and ultimately withdrew after resistance from fighters, collectively known as mujahadeen. Among them was Osama bin Laden. The US funneled arms and help to these anti-Soviet forces. But in the post-Soviet power vacuum, the Taliban was formed under the leadership of Mullah Mohammed Omar, who wanted to create an Islamic society, expel foreign influences like TV and music from the country and impose a repressive version of Islamic law that is particularly harsh on women. By 2001, they controlled nearly all of the country.
It was al Qaeda, the international terror network, not Afghanistan's Taliban -- a regional Islamic political and military force -- that attacked the US on 9/11.
But the masterminds of the attack, including Osama bin Laden, had been operating out of under the cover of the Taliban, which refused to give up bin Laden in the wake of the attack.
Support was nearly unanimous. The military effort was begun on authority from an "authorization for the use of military force" resolution passed one week after 9/11. Only one lawmaker, Rep. Barbara Lee of California, opposed it. That resolution was first used to authorize action in Afghanistan, but presidents since have leaned on it for action in at least 37 different countries, according to the Congressional Research Service.
The invasion, led by US forces with help from NATO allies, was framed specifically as a step in a war on terrorism.
"These carefully targeted actions are designed to disrupt the use of Afghanistan as a terrorist base of operations and to attack the military capability of the Taliban regime," he said, pointing out the name of the operation was "Enduring Freedom," although in hindsight it might be enduring war.
"Since September 11, an entire generation of young Americans has gained new understanding of the value of freedom and its cost and duty and its sacrifice," he later said.
Since then, a new generation of Americans has been born and come of age while the war that started that day carried on, often in the background with little focus from most of the public.
The number has fluctuated quite a bit. President Barack Obama came to office promising to refocus the US military there over Iraq, where Bush also invaded. At times during the Obama administration there were about 100,000 US troops deployed to Afghanistan. Obama tried to end US combat operations in Afghanistan in 2014, but left more troops in the country than he planned. His successor -- President Donald Trump -- sent new US troops there before largely drawing them down and engaging in peace talks with the Taliban.
The most deadly years were after Obama's surge of troops in 2009. The most deadly year for both the US and its NATO allies was 2010. There have been much fewer US deaths since major US and NATO combat operations ended in 2014.
By late 2001, bin Laden had moved through parts of Afghanistan and had crossed into Pakistan, where he would stay in hiding for nearly a decade until Navy SEALs killed him there in May 2011.
CNN's Nick Paton Walsh visited Taliban-controlled areas of Afghanistan that were the scene of US and British casualties a decade ago. He and his CNN team found women unable to go outside.
Paton Walsh writes: While Kabul and the center of most main cities remain mostly under government control, vast swathes of rural Afghanistan are ruled by the fractious and varied units of the Taliban. For more than five years now in Musa Qala, they have imposed their rules despite still being in regular conflict with Afghan security forces further south in Helmand province.
"At the end of the day the Taliban have the power," said one resident. "It is not really possible to go against their will."
The stated goal of the US involvement is not to liberate women repressed by the Taliban or to end that regime. In fact, the US has been involved in peace talks between the Taliban and the Afghan government for years.
The simplest explanation of the US goal in Afghanistan is to keep it from again becoming a hotbed for terror groups like al Qaeda. When the US left Iraq, for instance, the power vaccum helped lead to the rise of ISIS there.
But what the US has been trying to accomplish in Afghanistan, and the strategy to do it, has changed with each president.
That aimlessness comes through in an internal government study -- The Afghansitan Papers -- from 2015 that was uncovered and published by The Washington Post in 2019. It suggests government leaders have long misled Americans about what was achievable in Afghanistan.
In unvarnished interviews they never thought would become public, American military leaders told government viewers the US was unprepared for Afghanistan and that the American people did not know the "magnitude of dysfunction" in carrying out the war.
Very few US forces will be there and they will be focused on helping US diplomats. An exact number is unclear. It's not exactly clear, for instance, what role, if any, US special operations troops would play in Afghanistan.
Biden's decision is said to be final and not "conditions-based." This is happening.
There is bipartisan opposition.
"Apparently, we're to help our adversaries ring in the anniversary of the 9/11 attacks by gift-wrapping the country and handing it right back to them," said Senate Minority Leader Mitch McConnell on the Senate floor Wednesday.
Sen. Jeanne Shaheen, a Democrat of New Hampshire, tweeted when word of Biden's plans began circulating: "It undermines our commitment to the Afghan people, particularly Afghan women."
Related opinion: Biden is making a huge mistake on Afghanistan
There is support, particularly from progressives and Democrats.
"I think President Biden has come up with a careful and thought-out plan," Senate Majority Leader Chuck Schumer told John Berman on CNN's "New Day." "Look, John, the President doesn't want endless wars. I don't want endless wars. And neither do the American people."
"Year after year, military leaders told Congress and the American people that we were finally turning the corner in Afghanistan, but ultimately we were only turning in a vicious circle," said Massachusetts Sen. Elizabeth Warren in a statement.
It's also in line with Trump's aim of withdrawing from Afghanistan, although the former President has not weighed in.
While the US will continue to try to broker a peace agreement between the Afghan government and the Taliban, September may now be the de facto deadline for those talks. Biden is overruling military commanders who worry the Taliban will overrun the Afghan government once American firepower is gone. A US intelligence community assessment released Tuesday shares those concerns.
"The Taliban is likely to make gains on the battlefield, and the Afghan Government will struggle to hold the Taliban at bay if the coalition withdraws support," according to the official assessment of worldwide threats.
Biden said in his speech Wednesday that no amount of US forces on the ground can deter the Taliban or end the war.
"It was not true when we had 98,000 US troops on the ground, and it won't be true keeping [the current] 2,500 troops on the ground... We don't think they are a game changer," a source told CNN's Christiane Amanpour.
The US will still use diplomatic and monetary leverage. What's not at all clear is if those tools will get results where two decades of American military might have not.