The information box says that the han added 4,000 miles of wall. refer to the mileage scale. how can this be true?

the effect of the ming leaders banning ships with more than two masts was that there was no further construction of ships masts, because there was a surplus. ming emperors disallowed foreign exploration

answer:

it caused mass african migration, african populations to grow, african empires to topple, and racism against slaves to emerge.

the roman empire began to fall