The US is the 3th most populous country in the world..only behind China and India...do you think these other country allow foreign nationals to flood in to their country?
That's an interesting question. We know the Chinese are eager to get their hands on state prisoners, to use as scut labor, very much like the Southern prison-farm system 80 years ago, which grew up immediately after the Civil War. The Chinese arrest people on b.s. charges, just to stuff warm bodies into their prisons that they can then use as cheap labor. The Indians, not so much ..... but they still like indentured bond labor (Tata International got sued in the 90's for including what amounted to indenture clauses in some of their H-1B HR contracts with Hewlett-Packard, tho' I must confess I don't know how that lawsuit turned out), and they're especially fond of debt bondage and child slavery (those dhurri rugs, of which I blush to admit I own one, require tiny, dextrous fingers to weave properly).
So neither China nor India has clean skirts, and it's an open question whether their governments would smile on large-scale immigration from poor countries (Burma, say, or Nepal) to fill their workbenches and help depress wages below the pittance they've paid in the past (Chinese wages have been going up, causing some Stateside employers to repatriate jobs).