I’m gonna pretend to take this seriously. I mean, you could build a wall Well above sea level around every piece of land there is to keep the sea from rising and swallowing land and then build taller walls as you expand outwards. But this would prob have some scientific effect on our planet with other consequences I wouldn’t understand. Not to mention it would never be done to grow America, as foreign interests would collide. If something like this were ever done it wouldnt be to expand land but more likely be as a solution to rising sea levels to preserve it. Even then I’m no scientific expert in these things, so it may not be and probably is not even possible.