Note: All dates are B.C.
Pekah was the eighteenth king of Israel, ruling for twenty years, from 752 to 732 (the first twelve years of his rule were a co-regency with his predecessors). He is notable for an alliance made with Rezin, king of neighbouring Aram, and a subsequent invasion of Israel's sister kingdom of Judah, which precipitated an Assyrian invasion and conquest of Aram and Israel, and the eventual fall of Israel in 722.
The decline of Israel
In 752, Shallum assassinated his friend Zechariah, king of Israel, and usurped the throne. The general of the armies of Israel, Menahem, and another officer, Pekah, marched on the capital, Samaria, and killed Shallum in battle, usurping the throne for themselves. Shallum had been king for six months. Menahem was the official head of state, but Pekah shared the rule of Israel throughout the reign of Menahem and Menahem's son Pekahiah; Pekah was promoted to Menahem's former position as commander of the armies of Israel. At about this time, the prophet Hosea summed up current events:
On royal holidays, the princes get drunk. The king makes a fool of himself and drinks with those who are making fun of him. Their hearts blaze like a furnace with intrigue. Their plot smoulders through the night, and in the morning it flames forth like a raging fire. They kill their kings one after another.
Zechariah was the fourth king in the dynasty of Jehu, which had replaced the dynasty of Omri in 841, eighty-nine years previously. Since most Israelites of the time had lived throughout the ascension of the line of Jehu (the longest line of kings in Israel's history, which peaked with the reign of Jeroboam II, Zechariah's father) there was much resistance to the usurpers, and Menahem spent much of his rule violently repressing civil resistance.
During Menahem's reign, Tiglath-pileser III invaded Israel, but was bought off by Menahem, and Israel became a vassal state of Assyria. Tiglath-pileser, in his Annals, says of Menahem: "As for Menahem, terror overwhelmed him. Like a bird, alone he fled and submitted to me. To his palace I brought him back and...silver, colored woolen garments, linen garments...I received as his tribute."
The invasion of Judah
Menahem died of natural causes in 742, after ten years of rule, and Pekahiah inherited the throne. However, Pekah conspired against him, and in 740, at a banquet in the citadel in Samaria, assassinated him and became the sole ruler of the kingdom, the eighteenth ruler of Israel since Jeroboam I led the ten tribes of Israel away from Judah in 930, 190 years previously.
In 734, Pekah, his kingdom weakened by tributary payments to Assyria, as well as civil strife, formed an alliance with King Rezin of Aram in an effort to extract himself from Assyrian domination. They invaded Judah , intending to absorb her wealth and human resources to strengthen their own resistance. The capital, Jerusalem, was besieged, but did not fall, although other parts of Judah were annexed.
Isaiah the prophet, a member of the royal family in Judah, was there to record that "the news had come to the royal court: 'Aram is allied with Israel against us!' So the hearts of the king and the people trembled with fear, just as trees shake in a storm." Isaiah advised King Ahaz not to fear Rezin and Pekah, whom Yahweh regarded as "two burned-out embers". But Ahaz took no comfort in the protection of the God of his ancestors, and judging Judah's strength no match for the combined forces of Aram and Israel, petitioned Tiglath-pileser for support, emptying the Temple and his palace of gold and silver and sending it to the Assyrian ruler with the message: "I am your servant and your vassal. Come up and rescue me from the attacking armies of Aram and Israel."
The intervention of Assyria
After this message had been sent, but before it had been acted upon, Isaiah again tried to steer Ahaz on a course of trust in Yahweh, and proposed he ask for a sign that would prove he was eligible for the protection of God. But Ahaz wasn't interested in making deals with God, so Isaiah declared the famous prophecy:
The Lord himself will choose the sign. Look! The virgin will conceive a child! She will give birth to a son and will call him Immanuel--'God is with us.' By the time this child is old enough to eat curds and honey, he will know enough to choose what is right and reject what is wrong. But before he knows right from wrong, the two kings you fear so much--the kings of Israel and Aram--will both be dead.
Meanwhile, Tiglath-pileser, happy to receive Ahaz's payment of gold and silver, but already intending to invade Aram, Israel and Judah anyway, spearheaded a new invasion in 733. Aram, being the closest kingdom to Assyria, fell first. Rezin withdrew from Judah to defend his country, but was killed on his return to the capital, Damascus.
With the armies of Aram gone, Ahaz believed Judah could defeat Israel without the assistance of Assyria, and sent his forces to engage. But the Israelite warriors decisively defeated the soldiers of Judah in the battle, and returned to Israel with material plunder, as well as great numbers of enslaved woman and children. However, on their return to Samaria, confronted by a prophet about the trauma they'd dealt to their relatives of the two tribes of Judah, they gave the captives their freedom, even escorting them back to Jericho, a city in Judah.
The fall of Israel
Isaiah, for his part, had not been idle. Heeding the words of the prophecy he had uttered, he had gone ahead and fulfilled it in its immediate sense, and within a year he had a new son. At that point, inspiration struck again, and he delievered another of his well-known oracles:
The land of Zebulun and Naphtali will soon be humbled, but there will be a time in the future when Galilee of the Gentiles, which lies along the road that runs between the Jordan and the sea, will be filled with glory. The people who walk in darkness will see a great light--a light that will shine on all who live in the land where death casts its shadow.
This prophecy, too, would soon come to be fulfilled in an immediate sense. By 732, the Assyrians had completed their conquest of Aram, and continued on to Israel. All of northern Israel, from the Mediterranean Sea to the territories east of the Jordan River, fell to the Assyrian armies, and the inhabitants of these areas were exiled to various parts of the Assyrian Empire, as was Tiglath-pileser's policy (the conquered land was re-colonised by Assyrian expatriates).
Pekah was demoralised, and Tiglath-pileser supported Hoshea to supplant the king as ruler of Israel. Again in his Annals, Tiglath-pileser noted: "Pekah, their king, they had overthrown. I placed Hoshea over them." Hoshea, a friend of Pekah, conspired against him and assassinated him, becoming the final monarch of Israel.
In 722, the new Assyrian king, Shalmaneser, son of Tiglath-pileser, invaded Israel, exiled the remaining inhabitants, and resettled the land with more Assyrian colonists (from whom the Samaritans of later years were descended). Thus ended the northern kingdom of Israel, 208 years after its foundation.
The Bible, being a collection of all sorts of writings by all sorts of people, doesn't present the story of Pekah as nicely chronologically as I just have. I had great fun unravelling the story from all over the place, but if you're not inclined, here's a reading list for you to approach the story of the last days of Israel.