Another issue is that while Western Europe and those of Western European decent in the United States have a birthrate that puts our population in decline. The cultures that are pitted against us have a birthrate that causes their population to double every 30 years or so. What could go wrong? That issue alone means that we either build one hell of a wall and defensive system or we will be eventually overrun. It is simple demographics. Western culture is in rapid decline from a historical perspective even when compared with the plagues of the middle ages. Us old farts probably will not be around to see it all fall to pieces, but if our grandkids survive the onslaught, they are going to have one heck of a mess to clean up.
Demographics are destiny.
We have neither the “disposable” people nor the treasure to maintain the sort of empire the neocon asshats seem to want. Eff ‘em.