There are a few different definitions of 'terrorism':
. Systematic use of violence and intimidation to achieve some goal.
. Violence or the threat of violence directed against civilians for the purpose of creating intense fear, which the terrorist hopes to exploit to attain political or ideological goals.
. The systematic use of terror especially as a means of coercion.
You have:
. Timothy McVeigh and the Oklahoma City bombing in 1995.
. Charles Whitman, a shooter who positioned himself atop the observation deck at the Main Building tower at the University of Texas in 1966.
. Theodore Kaczynski, also known as the 'Unabomber', is an American mathematician, anarchist and domestic terrorist. Bombing period: 1978 - 1995.
I would say that the three listed above and Stephen Paddock are all homegrown American terrorists.