I worked in New Hampshire off and on for ten years. Boston was the "big city," and I used to escape there from time to time. Still have very good friends who live in the city. I remember the locals being a little hard to warm up to. They tended to look at people from other parts of the country -- let alone other countries -- as trespassers.
I learned the customs and language (I drove a "Toyoter") partly because I was on the radio and had to relate to the listeners, mostly just to fit in. After awhile, the locals came around and began to treat me like I was born there. (My oldest son actually was born there.) It probably also helped that, besides being on the radio, I am white and Christian.
I can see why those Chechnyan brothers might have had trouble fitting in, and why they might have wanted to get back at the those who didn't accept them. And I can see where they thought they could inflict maximum pain on the people they disliked by setting off bombs at the beloved Marathon on Patriots' Day, a very special day in the lives of Bostonians.
Besides picking the wrong way to deal with their problems, they picked on the wrong city. One of the reasons New Englanders take awhile to warm to you, one of the reasons it takes awhile to warm to them, is because they are genuinely tough. Could be the winters. Could be the ancestry. Whatever it is, you don't want to cross a New Englander. New Yorkers will spit in your eye, but a Southy will gouge them out.