I don't think that Western Civilization as a whole will fall in the next few hundred years, but the biggest threat to Western Civ in Europe is Muslim migration into the continent.  As birth rates decline in Europe, there is a need for labor to support the aging classes and to help maintain levels of living that Europeans are accustomed to.  Cheap labor is found in countries in Africa and the East.  As these immigrants continue to reproduce at a higher rate than native Europeans, they will eventually rival their hosts in numbers and influence.  Unlike Western Civilization, which is rather open and welcoming to people outside its value system, Muslim culture is not nearly as open and welcoming of ideas outside its parameters.  I'm not making a value judgment, just stating what seems to be an objective fact when we consider how Muslim culture is much more guarded and less permissive than Western Civ.  This means that Western Civ will dissolve in Europe and be replaced over the long term.

Whatever the fate of the West may be, its mark will remain on whatever replaces it via technology, legal traditions, political structures, and religion (namely Christianity).

That brings up a good point that I'll pose as a different thread topic.

As Newt Gingrich stated, we are already in the phony war stage of World War III which will be a war between East and West…a cultural/ideological/religious war.  The War on Terror is the catalyst that will ignite it.

The Middle East, Muslim world in general, seems to be a close menace but how many of these countries have the political or the military ability to challenge us ? Few if none. (Iran is trying) Not even talking about about philosophy or religion.

The military strategy of terrorism has put fear into us...and in that, they have succeeded.  But I do agree about China.  They may not be an actual threat yet, but they have the capability.  I still think the next major war is going to be either economic or over natural resources.

The immediate threat is radical Islam but the long range threat is China.  Give china 15-20 years and they will be a world power.  Unfortunately the west is playing right into their hands by buying anything and everything they make.  We are essentially financing our own destruction.  For a similar position economically you need look no further than England in the years prior to and during WWI.Of course, Muslims also pose a long range threat through their population growth and birth rate.  France is already seeing that with its large Muslim population, but they are not alone, most European countries face the same thing.  France is unlucky in that their Muslims are of Algerian extraction and so slightly more radical than those in Germany, Britain is pretty bad off with their large population of Pakistani extraction as well.I still think the existential threat comes from China though, the Muslims can blow up the occasional plane and building but they have proven unable to field effective armies for the past hundred years or so and I don't see that changing anytime soon.  Arabs are individually brave but collectively stupid when it comes to the military art.  There is a reason that the most successful people at spreading Islam by the sword have been Turks and Persians.

Cultural hegemony is the more insidious threat because it is more easily dismissed as a threat.  It is difficult not to see someone with a gun as a threat but someone preaching “tolerance or diversity” can sound reasonable and motives are harder to divine than intent.

But then, what comes after the Fall of the US?