Major attacks in U.S history are the Japanese attack on Pearl Harbor, the attack on the Alamo and the terrorist attacks of Sept. 11, 2001. The Pearl Harbor and September 11 attacks both led to an organized U.S. military response.
The attack on Hawaii's Pearl Harbor by the Japanese on Dec. 7, 1941, was a turning point that led the hitherto neutral United States to declare war on Japan and enter into World War II. Several Japanese fighter squadrons ambushed the base, killing or injuring several thousands of soldiers and sailors and destroying many planes and naval vessels. After the United States declared war, Japan, Germany and Italy declared war on the United States.
The Battle of the Alamo took place in Texas in 1836, where the army of Santa Anna attacked the Alamo fort. The fort defendants eventually perished at the hands of a group of Mexican soldiers, who broke in and destroyed most of the inhabitants.
Terrorists connected to a radical Islamic group known as Al-Qaeda carried out the attacks of Sept. 11, 2001. Their targets were major U.S. landmarks, specifically the Pentagon and the two largest World Trade Center towers. They carried out the attacks by hijacking and crashing commercial airliners into the buildings. Many believe that there was also a fourth target, as a fourth plane was also hijacked that same day, but passengers on board this plane realized what was going on, took over and crashed the plane into a Pennsylvania field. Some think that either the White House or U.S. Congress building was the original intended target.