How did America's population get so big when countries such as England are older but still have only about 20% of the US?

by therealow

I feel like the answer is obvious but it's eluding me.

DeSoulis

Because the amount of arable land in America is far larger than England's. The British population density is 262/km^2, much higher than America's 32.64/km^2. But because America has more land overall the population is higher.

therealow

Is that the same with most countries? How does that explain super dense populations like India? Is there no other reason?