Jamieson, Fausset and Brown on Habakkuk 3:7

7. the tents--that is, the dwellers.

Cushan--the same as Cush; made "Cush-an" to harmonize with "Midi-an" in the parallel clause. So Lotan is found in the Hebrew of Genesis for Lot. Bochart therefore considers it equivalent to Midian, or a part of Arabia. So in Nu 12:1, Moses' Midianite wife is called an Ethiopian (Hebrew, Cushite). Maurer thinks the dwellers on both sides of the Arabian Gulf, or Red Sea, are meant; for in Ha 3:6 God's everlasting or ancient ways of delivering His people are mentioned; and in Ha 3:8, the dividing of the Red Sea for them. Compare Miriam's song as to the fear of Israel's foes far and near caused thereby (Ex 15:14-16). Hebrew expositors refer it to Chushan-rishathaim, king of Mesopotamia, or Syria, the first oppressor of Israel (Jud 3:8, 10), from whom Othniel delivered them. Thus the second hemistich of the verse will refer to the deliverance of Israel from Midian by Gideon (Jud 6:1-7:25) to which Ha 3:11 plainly refers. Whichever of these views be correct, the general reference is to God's interpositions against Israel's foes of old.

in affliction--rather, "under affliction" (regarded) as a heavy burden. Literally, "vanity" or "iniquity," hence the punishment of it (compare Nu 25:17, 18).

curtains--the coverings of their tents; the shifting habitations of the nomad tribes, which resembled the modern Bedouins.

tremble--namely, at Jehovah's terrible interposition for Israel against them.