because they were attacking with weapons
mexican immigrants don't have catapults and battering rams
actually, the mongols just went around.
similarly, drug cartels will simply go around. the colombian cartels already use subs to get to mexico. who's to say they won't start using them to get into the US?
also, we'd be making human smuggling a lot more lucrative for the cartels now that buying a ticket through the cartels would become the only solution for people who don't intend on legal migration.
Plus the wall of china wasn't finished when the mongols attacked. Building a wall with modern methods and tech would probably go 100x faster.
modern methods would mean a wall far superior to the great wall of china in build quality, which partially eliminates the time reduction. it would also mean we can't use slaves, and workers we employ have standards.
mexico is practically a failed state already,
considering the severity of the still ongoing drug war. i sincerely doubt they'll be willing to pay for the wall, considering
the cost.
and there's not much of a chance that the US will fund it. congress is too busy funneling cash into their own wallets to care, and even if Annoying Orange wins the election, it wouldn't be by much. there'd be a lot of butthurt hillarites speaking out against it.
