Adam Clarke on Jeremiah 49:39

I will bring again the captivity of Elam - As this is to be in the latter days, probably it may mean the spiritual freedom which these people would receive under the Gospel dispensation. Under Cyrus, the Elamites, collected out of all quarters, were united with the Persians, their neighbors, and became, with them, masters of the east. See Calmet and Dahler. There are still, however, difficulties on this subject. Who the Elamites were is still a question. That which appears to be nearest the truth is, that the Elamites and Persians were two distinct people, and continued so till blended together under Cyrus. It is in this light that I have considered the subject in the preceding notes. Neighboring people are frequently confounded in history, and sometimes the name of a people is given to those who have the same character.