I think there has been. I'm not resolutely certain that it is an actual change in the environment more than a change in perception of it, though a case could be made for there being an actual change in some aspects of the physical threat environment we live in today.
The change in the threat environment can be stated in one sentence:
There is no safe place any more.
Now, it could be said that there never has been. What I think there have been before, though, are places that could be considered safer mainly because it was more difficult for criminals to reach them, and because society in earlier times enforced, sometimes overtly, the concepts of delineated neighborhoods and populations (the 'wrong side of the track' idea, basically). Those delineations have been broken down to a great degree (there is both good and bad in this as in many things). The main factor denying anyone a really safe place, however, is modern transportation. Criminals now can get in a car or hop on a bus and go from where there's nothing they can get to where there's everything they want. Business district, restaurant row, multiplex theaters, suburbs, small towns well outside the big-city limits, well-and-truly rural...name the area, the criminal can get to it without a great deal of trouble.
Demonstrations of this appear in the news reports from time to time. Communities that still keep their windows open and doors unlocked suffer predation, and yet more innocence (actually, it seems more like naivete nowadays) is lost. Horrific crimes are committed miles away from any so-called 'bad part of town'. There are still 'bad parts of town', sure, but the people in those parts are traveling to other parts to do their deed nowadays. After all, that's where the money and the murder and the raping is, and less chance of finding another predator or counter-predator there than around where they live.
There is no safe place any more. To not fully realize this is to risk being completely and utterly surprised and very off-balance instead of perhaps still suffering some surprise but not enough to keep you from acting immediately and decisively to counter the threat against you and yours.
Now, some reading this are going to take it the wrong way at first. "No safe place? I have to be looking for an attack everywhere? That's paranoid! I will NOT live my life in fear!"
I can see it coming, so let me make something clear: No paranoia required, no living in fear needed, to adequately and (I would say) relatively easily increase your level of safety and preparation. Absolutely no need for anything like that. Fearfulness and paranoia (clinical or not) are actually going to be quite counterproductive to you, in fact. So let's not go there, please.
How, then, to respond to this? How, then, to think about it?
First, acknowledge the reality that bad things can happen to good people even in good places. It can't be a surface or intellectual acknowledgement if it's going to do you any good. Has to be more a quiet realization that there's a possibility of Bad Things Coming no matter where you are at the time. This is the most important step, one many people have not taken even knowing they should.
Once that's done, the next step is to make a rather subtle attitude change. It may happen when the quiet realization is made, or it may have to be adopted consciously. I'm afraid I'm going to have trouble describing this simply or easily, and I may have to come back and change it after I've done it to make it clearer, but here goes: There's an element of low-level background skepticism about most places, most people, most situations and environments you go through. It's not strong, it's not something that takes your attention unless something specific raises a flag. You'll have to look for it consciously to find it. It will be there, though, and you will see its affects mainly in the way your outlook and your posture and position (non-physical mostly, but it could affect the physical as well) changes in relation to places, people, and relationships (business and personal). You'll find yourself setting things up, here and there, now and again, improving your position against the possibility of surprise attack. It's not the same thing as Situational Awareness, but it will, probably, have some affect on that among other things. It's possible you won't notice the changes this attitude is driving for a while. You'll just realize one day that your outlook and some of your habits large and small and some of the choices you make are different than they used to be. Then you get to decide if that's okay or not. Then you either change it back and go on about your life or just go on about your life.
People like Roger Phillips and glockman10mm can probably explain this better than I can. There are others, of course, people that have lived in higher-threat environments than I have for a long time, but I know those two have. Others who have and who will comment on this, please do so.
The great news about this is that it doesn't have to change anything significant. You can still give people you meet the benefit of the doubt. You can still trust someone or some group as much as you want. You don't have to cut people out or change the way you take to them or anything. You can still go where you want and do what you want. No 'bunkering up', mental or physical, to it. Make the realization, adopt the attitude, maybe some things change, maybe they don't, but you're still living your life the way you want to live it.
Some of you will wonder why I'm stating the obvious here. Fact is, even some here haven't fully realized the reality of the threat we're all facing. And some who have reject it because they think it means they have to go all paranoid 'n stuff once they accept it. So I want to make sure it's stated, and that it's clear that you can still live with it.
So there it is. Increased security and preparedness and you get to live your life like you want still.
What's not to like about that?
Note: I may be completely freakin' wrong about all of this. Don't hesitate to say so if you think so. I'd like to hash this concept out one way or the other.