The answer is :
The Earth is round all the way to the inner core out.
Turkish, Arab, Persian, and African <span>cultures.</span>
Internal terrorism and external terrorism both pose a great threat, but terrorism carried out by the United State's own citizens can be much more harmful in the long run. My favorite quote about this is nerdy, but it's from Captain America: Civil War and is stated by the true antagonist of the movie, "An empire toppled by its enemies can rise again. But one which crumbles from within? That's dead... forever." We as a people can rally against an outside threat and rise from whatever they may do to us, but we become exponentially weaker if we must rally against those within our own borders. That's just kinda my opinion.