"Our mission in Afghanistan was never supposed to have been nation building.  It was never supposed to be creating a unified, centralized democracy," Biden said in an address to the nation.

Biden's approach to the conflict of pulling out US troops has raised questions about his ability to handle the situation.

Responding to the same, Biden said: "We went to Afghanistan almost 20 years ago with clear goals: get those who attacked us on September 11th, 2001, and make sure al Qaeda could not use Afghanistan as a base from which to attack us again."

"Our only vital national interest in Afghanistan remains today what it has always been: preventing a terrorist attack on American homeland," he said.

Brushing off criticism that the evacuation is a debacle, he said, "I stand squarely behind my decision.  After 20 years, I’ve learned the hard way that there was never a good time to withdraw U.S. forces."

"That’s why we were still there.  We were clear-eyed about the risks.  We planned for every contingency," he added.

Biden stated that when he came into office, he inherited a deal that former President Donald Trump negotiated with the Taliban. 

"Under his agreement, U.S. forces would be out of Afghanistan by May 1, 2021 — just a little over three months after I took office. U.S. forces had already drawn down during the Trump administration from roughly 15,500 American forces to 2,500 troops in country, and the Taliban was at its strongest military since 2001," he said.

"The choice I had to make, as your President, was either to follow through on that agreement or be prepared to go back to fighting the Taliban in the middle of the spring fighting season," he added.

However, he agreed that the situation took a turn more soon than the US had predicted.

"But I always promised the American people that I will be straight with you.  The truth is: This did unfold more quickly than we had anticipated," he said.

"If anything, the developments of the past week reinforced that ending U.S. military involvement in Afghanistan now was the right decision," he said.

Biden said American troops cannot and should not be fighting in a war and dying in a war that "Afghan forces are not willing to fight for themselves."

"We spent over a trillion dollars.  We trained and equipped an Afghan military force of some 300,000 strong — incredibly well equipped — a force larger in size than the militaries of many of our NATO allies," he said..

Biden blames Afghan administration:

The US President said his country had given them (Afghanistan government) every chance to determine their own future. 

"We gave them every tool they could need.  We paid their salaries, provided for the maintenance of their air force — something the Taliban doesn’t have.  Taliban does not have an air force.  We provided close air support," he said, adding "What we could not provide them was the will to fight for that future.."

He said it is wrong to order American troops to step up when Afghanistan’s own armed forces would not.

"If the political leaders of Afghanistan were unable to come together for the good of their people, unable to negotiate for the future of their country when the chips were down, they would never have done so while U.S. troops remained in Afghanistan bearing the brunt of the fighting for them," said the US President.

He said Afghanistan President Ashraf Ghani had spoken how the country should prepare to fight their civil wars after the U.S. military departed, to clean up the corruption in government so the government could function for the Afghan people.

"They failed to do any of that," he said, adding that Ghani insisted the Afghan forces would fight, "but obviously he was wrong".

"So I’m left again to ask of those who argue that we should stay: How many more generations of America’s daughters and sons would you have me send to fight Afghans — Afghanistan’s civil war when Afghan troops will not? "

"I’m clear on my answer: I will not repeat the mistakes we’ve made in the past — the mistake of staying and fighting indefinitely in a conflict that is not in the national interest of the United States, of doubling down on a civil war in a foreign country, of attempting to remake a country through the endless military deployments of U.S. forces," he said.

Biden said what is happening now could just as easily have happened 5 years ago or 15 years in the future. 

"We have to be honest: Our mission in Afghanistan has taken many missteps — made many missteps over the past two decades," he said.

"I’m now the fourth American President to preside over war in Afghanistan — two Democrats and two Republicans.  I will not pass this responsibly on — responsibility on to a fifth President," he said.

Biden said will not mislead the American people by claiming that just a little more time in Afghanistan will make all the difference. 

"Nor will I shrink from my share of responsibility for where we are today and how we must move forward from here. I am President of the United States of America, and the buck stops with me," he said in a clear message.

"I know my decision will be criticized, but I would rather take all that criticism than pass this decision on to another President of the United States — yet another one — a fifth one," he said in the face of severe criticisms about his "failed leadership".

Biden pledges to support Afghan people:

However, he promised to continue to support the Afghan people. "We will lead with our diplomacy, our international influence, and our humanitarian aid. We’ll continue to push for regional diplomacy and engagement to prevent violence and instability," he said.

"We’ll continue to speak out for the basic rights of the Afghan people — of women and girls — just as we speak out all over the world.

"We’ll continue to push for regional diplomacy and engagement to prevent violence and instability. We’ll continue to speak out for the basic rights of the Afghan people — of women and girls — just as we speak out all over the world," he said.

Standing firm behind his decision, he stressed that: "I am deeply saddened by the facts we now face.  But I do not regret my decision to end America’s warfighting in Afghanistan and maintain a laser-focus on our counterterrorism missions there and in other parts of the world."

"I cannot and I will not ask our troops to fight endlessly in another — in another country’s civil war, taking casualties, suffering life-shattering injuries, leaving families broken by grief and loss," he said.