What conflict caused Israel to split into two kingdoms?

Answer 1

Rehoboam's father, King Solomon, had levied relatively heavy taxes, which had been used for such large-scale endeavors as building the First Temple. The fact that the nation was so prosperous and happy in his time (1 Kings 4:20) demonstrates that Solomon conducted his governance in a praiseworthy manner.
After Solomon's death, the people approached his son Rehav'am (Rehoboam) and asked that he now lower the tax. He ignored the counsel of his elder advisers and refused the people's request. This led the Ten Tribes to turn away from him (1 Kings ch.12).
The background reason was because King Solomon had been less than perfectly righteous. This led God to punish him by diminishing his dynasty in the lifetime of his son (Rehoboam). 1 Kings ch.11. A deeper reason is that God wanted the more righteous people of Judah to be influenced by the Ten Tribes as little as possible.
Centuries later, by 738 B.C.E., both kingdoms faced new threats to their independence from the Assyrians. The Assyrians forced Israel and Judah to pay tribute. In 722 B.C.E., Assyria invaded Israel, whose army was weak, and conquered it. The kingdom of Israel ended. Around 612 B.C.E., the Assyrian Empire fell to the Babylonians.
For many years, King Nebuchadnezzar ruled Babylonia. In 586 B.C.E., Nebuchadnezzar captured Jerusalem. When Judah's leaders resisted his rule, the Babylonians destroyed the Temple in Jerusalem. They took hundreds of thousands of Jews to Babylon, some as slaves.

Answer 2

After Solomon's death, the people approached his son Rehav'am (Rehoboam) and asked that he now lower the tax. He ignored the counsel of his elder advisers and refused the people's request. This led the Ten Tribes to turn away from him (1 Kings ch.12).

See also the Related Links.

Link: Where are the Ten Lost Tribes

Link: List of kings

Link: Solomon's errors