Battle of Mount Zemaraim

The great Battle of Mount Zemaraim was reported in the Bible to have been fought in Mount Zemaraim, when the army of the Kingdom of Israel led by the king Jeroboam I encountered the army of the Kingdom of Judah led by the king Abijah I. About 500,000 Israelites were said to lay dead in a single engagement, though most modern commentators consider the numbers to be either wildly exaggerated or symbolic, and some have even questioned its fundamental historicity. The modern calendar date is, of course, not given in the Bible, though in the chronology proposed by Thiele, it can be referred to around 913 BC.

Background
The friction all began when the late king Rehoboam increased the royal taxes throughout the Kingdom of Israel after Solomon died in about 931 BCE. This created discontent among all the Israelite tribes of the kingdom, excepting Judah and Benjamin, and the people's discontent soon became a rebellion when the king, against the advice of the elders, refused to lessen the burdens of royal taxation. The ten northern tribes of Israel eventually broke up from the kingdom and made a new Kingdom of Israel with the former fugitive Jeroboam as king, provoking a civil war. Rehoboam then went to war against the new kingdom with a force of 180,000 soldiers. However, he was advised against fighting his brethren, and so returned to Jerusalem.

Prelude
Ever since the unified kingdom was divided, there has been constant border issues between the two parties, and both attempted to settle them. Abijah succeeded his father Rehoboam to the throne after the latter died. According to Biblical sources, Abijah has an army of 400,000, all of them handpicked ones, and Jeroboam has 800,000 brave warriors with him.

Battle
Before the battle, Abijah addressed the armies of Israel, urging them to submit and to let the Kingdom of Israel be whole again. As written in the 2 Chronicles 13:4-12, Abijah then rallied his own troops with an address to all the people of Israel:

Abijah's phrase "God is with us as our head (or leader)" became famous since that event. However, his plea to the people fell on deaf ears.

Jeroboam had set up an ambush to come from the rear of Abijah's army, so that the latter's army would be fighting on his army's front and rear. Then all of the soldiers of Judah plead to God for help, and then the priests blew the trumpets. Abijah was quick in countering this move made by Jeroboam; he executed a pincer movement to crush the latter's huge army.

The elite warriors of Judah then executed a pincer movement to rout Jeroboam's troops as Abijah planned, killing 500,000 Israelite warriors in the process. The rest of the Israelite army fled from the battlefield heading back north, and the forces of Judah then pursued them, taking the cities of Bethel, Jeshanah and Ephron during the ensuing pursuit. The factor for Judah's success in the battle is mainly attributed to Abijah and his troops' unswerving trust and faith in the LORD God.

Aftermath
Jeroboam was crippled by this severe defeat to Abijah and thus posed little threat to the Kingdom of Judah for the rest of his reign. But, though victorious, Abijah also failed to unify Israel and Judah. The two kingdoms would be engaged in severe border wars for almost two centuries until the latter's destruction by Assyria in 720 BC.