Historically the Chaldeans were a seminomadic people from Arabia who occupied the city of Ur “of the Chaldeans.” (Genesis 11:28) and neighboring lands.
They are referred to in the accounts of Assyrian kings that date back to 884-859 BC. In 721 BC, a Chaldean ruler, despite great opposition, seized the throne of Babylon and reigned for ten years. Isaiah 39 tells of his efforts to excite the western states against Assyria. In 597 and 586 BC, under Nebuchadnezzar II, they conquered Judaea and captured Jerusalem. The Chaldean dynasty continued until the Persian invasion of 539 BC.
The country of Chaldea< was an ancient land in southern Babylonia, on the Persian Gulf near the delta of the Tigris and Euphrates rivers. In the Biblical times the name was applied to all of Babylonia.