What major event occurred on September 11, 2001, in the United States?

The major event that occurred on September 11, 2001, was a terrorist attack in New York City. This day is marked by coordinated attacks carried out by the extremist group al-Qaeda, which involved the hijacking of commercial airplanes. Two of these planes were flown into the Twin Towers of the World Trade Center, leading to their collapse, while a third plane struck the Pentagon. Additionally, a fourth plane, United Airlines Flight 93, was headed for another target in Washington, D.C., but crashed in Pennsylvania after passengers attempted to overcome the hijackers. This event had profound implications for national security policies, international relations, and led to significant changes in American society, including the initiation of the War on Terror.

In contrast, the other options represent significant events in history but did not occur on that particular date. The first manned landing on the moon took place in 1969, major earthquakes in California have happened at various times throughout history, and the election of the first African American president, Barack Obama, occurred in 2008. Each of these events is notable but is unrelated to the September 11 attacks.