1 The USA has a population of 326.8 million (Britain has a population of 65.6 million people)

and

2 The USA has a landmass of 3.797 million sq. miles (Britain is 80.823 sq. miles)

and

3 Therefore the USA needs a gigantic wall to stop it from being swamped.

BUT

If the USA had Britain’s population density they’d have a population of 15,453,600,000 people, which is just about twice the world population. 

Chris