Jamieson, Fausset and Brown on Jeremiah 31:36

36. a nation--Israel's national polity has been broken up by the Romans. But their preservation as a distinct people amidst violent persecutions, though scattered among all nations for eighteen centuries, unamalgamated, whereas all other peoples under such circumstances have become incorporated with the nations in which they have been dispersed, is a perpetual standing miracle (compare Jr 33:20; Psa 148:6; Is 54:9, 10).