Why did the Medes and Chaldeans join forces in 612 B.C.?

The Medes and Chaldeans joined forces in 612 B.C. primarily to overthrow the Assyrian Empire, which was in decline but still a dominant power in the region. The alliance was strategically beneficial; the Medes sought to expand their territory and influence, while the Chaldeans aimed to liberate their homeland, Babylon, from Assyrian control. Together, they successfully captured the Assyrian capital of Nineveh, marking a significant turning point in Mesopotamian history. This collaboration ultimately led to the rise of the Neo-Babylonian Empire.