Chaldea was a marsh tribe, not all of Babylonia
Between the eleventh and ninth centuries BC, West Semitic Kaldu settled the southeastern marshes of Babylonia. Hebrew and Greek writers later stretched Chaldea across the whole south—a geographic misnomer—yet a dynasty linked to them still ruled Babylon from 626 to 539 BC.
During Babylonian weakness, Suteans and Arameans arrived from the Levant first; about a century later came the Kaldu, remembered as Chaldeans. They camped chiefly on the Euphrates' left bank in the far southeast. Neo-Assyrian texts call the sporadically independent migrant territory mat Kaldi from the early ninth to late seventh centuries BC, reaching the Persian Gulf's western shores under Assyrian domination (911–605 BC). Bit Yakin, largest of five Chaldean tribes, stretched from the lower Tigris toward Arabia; Sargon II said it reached Dilmun. Tribal capital Dur Yakin was Marduk-Baladan's seat.
From 626 to 539 BC a ruling house later labeled the Chaldean dynasty governed the Neo-Babylonian Empire at its height, though final king Nabonidus may not have shared that origin. Akkadian mat Kaldu or Kašdu underlies Greek Khaldaía and Latin Chaldaea; Hebrew Kaśdim names both land and people. Genesis lists Kesed among Nahor's sons; Josephus linked Arpachshad to Chaldeans. Despite the echo, ancient Chaldea is not the modern Chaldean Catholic Church, whose adherents are mostly ethnic Assyrians—and some Assyrians argue Mandaeans keep stronger demographic ties to the old marshes.
The label stuck because outsiders needed a short name for southern Mesopotamia's late kingdoms. Precision still matters: Chaldea proper was the estuary country, not every acre of Babylon. Confusing the part with the whole is how a tribal marsh became a biblical synonym for empire.
Source: Chaldea
