The Germans sabotage bombed a bunch of stuff during WWI. 9/11 was al-Qaeda's second or third attack on the WTC specifically. There were dozens of wars between the US and indigenous nations over the centuries. Then there's all the false flag bullshit, domestic terrorism, The American Civil War, tons of insurgency shit like the KKK, the regulators, bleeding kansas, Jim Crow, All the fighting and terrorism during the Civil Rights years.

Edit: and the huge amount of "terrorism" during the Vietnam war years, just constant bombings that have been swept under the rug of the US's public memory of the Vietnam War era.