In 100 years, every nation on this planet will have the ability to destroy all of humanity with ease. There will still be Osama Bin Ladens - I truly doubt that man will ever reach the stars because of these facts.
I believe Sagan was right when he posited that "advanced" civilizations, by definition, will wipe themselves out (long before interstellar travel is achieved).
re where are they: Everywhere. Just cloaked. Duh!
It doesn't even have to involve a huge destructive war. Just look at how the Vietnam war sucked all the resources and interest out of landing on the moon, and how WTC911 has converted the space program to military goals already. And that is without any actual crippling damage to the infrastructure. How can we possibly go to the stars when infants such as bin Laden are whining for attention all the time?