The Last Enemy...is ourselves.
In a world in which we've "won", become safe from the danger that at any moment we will be attacked, be it by wild animals or violent invaders, what do we fear? A change in the status quo? A falling from the pinnacle? When we reach the hegemon's seat...whom shall we fear? It becomes, when no outside force is our military equal, and our cities are generally free from outside danger, that the focus turns inward. The last enemy lies within. It is ourselves. It is our citizens. It is the non-conformist. It is the neighbor across the street or the odd-looking quiet man in the alcove of the apartments across the way. It is and always shall be...the pitfall of utopia and of humanity.