Okay, Vicki, I promised a long time ago to reply, you convinced me lol.
To my mind, humanity's worst enemy's its own greedy. I believe that's the source of all evil, maybe I'm wrong... but let me explain my theory.
It's due to this blind sought after power that this vicious circle's started. You DO have a point Vicki, terrorism is terrible, but then again, I believe it's only a consequence of human's greedy. When searching for absolute power, men become depotists, from there on they can do anything... They get people who are hopeless or at least, feel that way and make them believe that by joining some religions, the traffic, terrorist groups, etc (whose only aim are to get more power and more money) they'll find salvation. Fact is, they aren't entirely to blame, because their values get lost in between all this mess and nothing much is salvagable anymore. Thus, they wind up losing all fear and ppl who have nothing to fear, have nothing to lose, so they'll literally go to the ends of the earth to accomplish their aims. So... the harmful circle of hate, greedy, power and fear's formed... Those like us who have ppl and things to lose, get scared and are slaves to the big mafia bosses, terrorists, preachers of war, etc... The latter who are VERY feaful and coward as they DO have sth to lose as well.... End up using the ones bellow them in the ladder as their weapons and shields. Lack of education, opportunities, etc, certainly contribute to it....
To sum up, I'd say this insatiable sought for power's the biggest problem facing the world.... Though in my humble opinion it isn't recent.... has always been this way, since our dear cavemen.