Osama bin Laden, the leader behind the terrorist attacks of September 11, 2001, in which almost 3,000 people died in New York, Virginia and Pennsylvania, was killed Sunday by U.S. troops in Pakistan.

When President Barack Obama announced the death of the leader of the terrorist group al-Qaeda (pronounced: al-Kye-da), Americans cheered and wept, and thousands gathered at the White House and at the site of the attack in New York, waving flags and singing the national anthem.

In speaking to the country in a rare Sunday night appearance at the White House, the president said that the killing of bin Laden, nearly 10 years after his most infamous terrorist attacks, serves as a reminder that “America can do whatever we set our mind to. This is the story of our history.”

KidsPost’s Tracy Grant answers some questions you might have about the killing of Osama bin Laden.

So who exactly was bin Laden?

He grew up in a wealthy Muslim family from Saudi Arabia. As a teenager, bin Laden became very religious. In the 1980s, he viewed the invasion of Afghanistan by the Soviet Union (which has now become several separate countries, including Russia) as a religious war. In the 1990s, when the United States fought against Iraq after Iraqi troops invaded neighboring Kuwait, bin Laden began to see the United States as an enemy of the Muslim faith and people as well. While most Muslims do not share his view, he organized a network of terrorists who agreed with him, then launched attacks on U.S. embassies in the 1990s and on a U.S. warship in 2000. He was 54 when he was killed.

What happened on September 11, 2001?

Terrorists from bin Laden’s group hijacked four airplanes. Two were flown into the World Trade Center skyscrapers, also known as the Twin Towers, in New York City. One was flown into the Pentagon in Virginia. Passengers on the fourth plane, who had heard about the other attacks, tried to take back control of their plane from the hijackers, and it crashed in Shanksville, Pennsylvania. It is believed that the hijackers intended to fly the plane into a building in Washington, perhaps the White House or the Capitol.

Almost 3,000 people died that day; it was the worst terrorist event ever in the United States. Shortly after the attacks, President George W. Bush announced the U.S.’s goal to get bin Laden, “dead or alive.”

Did things change after the attacks?

Many KidsPost readers weren’t even alive on September 11, 2001, or are too young to remember it, so they don’t realize how much life has changed since the attacks. Airport security is much tighter than before. You are required to take your shoes off at the airport because an al-Qaeda terrorist tried to sneak explosives onto a plane in his shoes after September 11. Security at government buildings is also much more strict.

Also, the United States went to war in Afghanistan to try to capture bin Laden and destroy al-Qaeda.

Why did it take so long to find bin Laden?

Many people thought bin Laden would be captured soon after the attacks, and U.S. forces got very close to him several times. But he proved to be very good at hide-and-seek, often hiding in rural areas in Afghanistan and Pakistan. When new information came in about where bin Laden was, President Obama ordered U.S. forces to attack.

So does this mean we don’t have to worry about terrorists anymore?

Unfortunately not. Al-Qaeda isn’t the only terrorist group in the world, and even with bin Laden dead, al-Qaeda still exists. Bin Laden hasn’t been the day-to-day leader of al-Qaeda for a while. But he was the inspiration for many evil acts. Since the September 11 attacks, the government keeps trying to find ways to stop attacks before they are carried out.

Why are many Americans happy that bin Laden has been killed?

It’s not quite happiness, but a sense of relief and fairness. Bin Laden was responsible for the deaths of thousands of innocent people. As President Obama said on Sunday night, “On nights like this one, we can say to those families who have lost loved ones to al-Qaeda’s terror: Justice has been done.”