It is going to happen again. It is just a matter of who, where, and when. I don't expect it to be the big cities this time. The have too many resources paid for with funds distributed in the last ten years. A Mumbai style attack in New York, with over 30,000 police officers, multiple SWAT teams etc is a losing proposition. A Mumbai style attack on a couple of outlet malls scattered around the country in counties that might only have five deputies working on a shift is more likely. The small towns where people feel safe because nothing ever happens there. The ones that obviously wont be targeted because they are too small. The ones that don't have the resources locally and have to call the state police for a SWAT team.
Part of the problem is that we expect a certain standard of living in this country. One that many in the world are envious of. To maintain that standard of living our government negotiates trade agreements, unfair in the eyes of many, that give our corporations every advantage possible. Our corporations, to be able to sell those wonderful things we all just can't live without at a reasonable price and still make a profit, "exploit" workers in other countries. It doesn't matter that we are paying the workers three or five times what they made before. Because by doing this we are running the other local employers out of business. So we are evil for paying them less than we would an American worker. We are evil for paying them too much because no one locally can compete for the workers.
For our electronics we "steal" raw materials from around the world. And we just can't win. Before we were "stealing" the raw materials no one was buying them (at least in the quantities we do) so the local economies were getting nothing. If we paid what some claim we should, the materials costs of the products become so high that the price goes with it and so demand falls off, so we don't "steal" as much from them and the local economy is in the toilet again.....
Our government, to protect our interersts puts pressure on other governments. We either threaten to withhold foreign aide, or maybe hint at an arms deal with a not so friendly to them neighbor. We support dictatorships. We support insurgencies against governments we don't like. As Van Halen pointed out in a video, right now our government is doing things we think only other countries do.
As I see it we only have a couple of options. Revise our expectations as to our standard of living and accept that maybe we can't have everything we want when we want it.
Or, we can get serious ( Sun Tzu serious) about killing the people that hate us so much. That would mean being as subtle and half as diplomatic as Joe Stalin. It could very well also mean turning the majority of the civilized world against us. As has been demonstrated throughout history, it is not always the most powerful that win. Sometimes it is just a matter of being willing to do that which your opponent is not.
Or we can accept it as the cost of doing business and just keep on doing what we have been doing.