Walled States, Waning Sovereignty

Why, just two decades after international celebrations of the fall of the Berlin Wall, are so many nation-states building elaborate walls at or near their borders? Why walls now, given growing global connectedness and given the general imperviousness of late modern powers — from capital to religion to terror — to physical blockading? How do walls shore up an imago of sovereign statehood and to what extent do they fortify reactionary national imaginaries? What do the new walls perform symbolicall