THIS MIGHT SURPRISE YOU
The answer
Assyria, in 722 BCE. Assyrian policy deported a substantial segment of the population — especially ruling, military, and skilled classes — and resettled others in their place, though many inhabitants remained and settlement continued. The deportations gave rise to the later legend of the "ten lost tribes," which is a legend rather than a record of a people vanishing. Judah in the south survived more than a century longer.
Why it’s interesting
Two kingdoms, two falls, to two different empires — Israel to Assyria in 722, Judah to Babylon in 586. Keeping the two straight untangles a lot of Old Testament history.
Scholarly consensus
You can know the Bible.
Not just the stories, but the history, authorship, and scholarship behind it.