The time of my story is about 100 years from now. between 2020-30 a huge war started which lasted a few decades. At the end of the war, America decides to divide into 3 nations (at least), all having different laws and leaders (i'll have at least one nation being republic). I want a nice big wall to separate the nations. But would it actually be possible to build a huge wall stretching across America? I've thought about only having the richest nation having a wall, so that they're cut off from everyone else. Bear in mind that there would've been thousands of builders working on the wall.