"Shall we expect some transatlantic military giant to step the ocean and crush us at a blow? Never! All the armies of Europe, Asia, and Africa combined could not by force take a drink from the Ohio River or make a track on the Blue Ridge in a trial of a thousand years. At what point then is the approach of danger to be expected? I answer. If it ever reach us it must spring up amongst us; it cannot come from abroad. If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide."
~ An American president who was shot by an American citizen on 1865-04-14
We have the largest quantity of immigrants in our country than anywhere else in the world. 50+ million immigrants that all bring their varied experiences and war is a part of many of their stories.
Over the last 200 years, at least, how many major conflicts have started for secular politics vs religious politics. I feel there is a heavy skew towards the former.
Also if you want to get really nit picky one could argue 9/11 was more motivated by geopolitics.