Gender: Male Location: The Fortress of Solitude in Venus
It didn't help the Chinese vs the mongolian invasion that is for sure.
As for working or not. With the invention of gunpowder walls became obsolete in medieval warfare.
Now if you reffer to the great wall of Mexico that Trump wants to build, it is a useless expenditure as IIRC 40 or 60 % of undocumented workers came by plane
So my take on it is that yes they are useless, take it from me who install security cameras. No matter how high or big the wall is there is always someone who will pass it
Also we do mass trade with the country via trucks and cars and ships. They're one of our biggest trade partners because they're a friendly trillion dollar economy who is right there.
Also-also, we don't actually have much immigration from there nowadays.