He increaseth the nations, and destroyeth them - He has entire control over them. The sources of prosperity are in his hand, and at his pleasure he can visit them with famine, pestilence, or war, and diminish their numbers and arrest their prosperity. Dr. Good renders this very improperly, “He letteth the nations grow licentious;” but the word שׂגא śâgâ' never has this sense. It means, to make great; to multiply; to increase.
And straiteneth them again - Margin, “leadeth in.” So the word נחה nâchâh means. The idea is, that he increases a nation so that it spreads abroad beyond its usual limits, and then at his pleasure leads them back again, or confines them within the limits from where they had emigrated.