"What are they afraid of?"

Have you not been paying attention in the last 50 years? We've made a hell of a lot of enemies, and before that it was communism, and before that it was world wars. Our military is strong because if it wasn't we would be getting attacked constantly. I'm pretty sure that a major reason why there haven't been any substantial terrorist attacks on the US since 9/11 is because our military will FUCK UP ENTIRE COUNTRIES if that happens again. Shit, we got launched into a 6-year war with 2 countries after an independent terrorist group blew up our building. If the KKK went to another country and bombed a building, would that country then attack and occupy us? Absolutely not! Because they can't.