NAFTA only increased the U.S. GDP by a few hundredths of a percent because relative to the size of the total economy, trade with Mexico and Canada isn't that big.
The gap can be 100 to one in some cases if you simply measure the gross national product per person in the United States versus, say, a country in Africa, maybe a gap of $30,000 per person and $300 per person.
They need more. But, despite that investment, the GNP growth per capital in the countries of sub-Saharian Africa has been negative, on average, for a decade.