The crimes of Solomon's son Rehoboam.
Rehoboam goes to Shechem to be crowned king. Jeroboam hears about it in Egypt and comes running to plead with him to ease the forced labour Solomon has imposed on the Israelites. Rehoboam asks for a few days to think. His father's advisors promise him that if he relaxes the labour, the Israelites will become his loyal followers. However his contemporaries advise him to say his little finger is thicker than their fathers', uh, thighs. Yup, that's so what a dude would compare his little finger to. Nope, not to a dick at all. They also advise him to say he's going to add to their burdens and whip them with scorpions. Scorpions are so creepy!
When Jeroboam comes back, Rehoboam repeats his lackeys' advice, which was god's plan all along. The people renounce him as their king and go home, but the ones who live in Judah are still in Rehoboam's territory. They prove quite restful: Rehoboam sends an official out to collect taxes, whom they stone to death. Rehoboam doesn't need any more prompting and flees to Jerusalem.
The stoning was the opening salvo in a civil war. Judah stays loyal to Rehoboam, but the other tribes declare Jeroboam their king.
Rehoboam raises an army of 180 000 (the same size as the modern Greece's army), but god orders Shemaiah the holy man not to attack his brethren.
Meanwhile, Jeroboam builds some cities and worries the people's loyalty will shift back to Rehoboam if they go and worship at the temple in Jerusalem. So he goes ahead and builds two golden calves. You know, those things Aaron built that caused all those deaths back in Exodus. The people worship the calves, but god is oddly silent this time, even when Jeroboam makes non-Levites priests and makes up new holidays.