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Downfall and demise of the kingdom

After this date, the power of both the Hittites and Egyptians began to decline yet again because of the power of the Assyrians. The Assyrian king Shalmaneser I had seized the opportunity to vanquish Hurria and Mitanni, occupy their lands, and expand up to the head of the Euphrates, while Muwatalli was preoccupied with the Egyptians. The Hittites had vainly tried to preserve the Mitanni Kingdom with military support. Assyria now posed just as great a threat to Hittite trade routes as Egypt ever had. Muwatalli's son, Urhi-Teshub, took the throne and ruled as king for seven years as Mursili III before being ousted by his uncle, Hattusili III after a brief civil war. In response to increasing Assyrian annexation of Hittite territory, he concluded a peace and alliance with Ramesses II (also fearful of Assyria), presenting his daughter's hand in marriage to the Pharaoh. The Treaty of Kadesh, one of the oldest completely surviving treaties in history, fixed their mutual boundaries in southern Canaan, and was signed in the 21st year of Rameses (c. 1258 BC). Terms of this treaty included the marriage of one of the Hittite princesses to Ramesses.

Hattusili's son, Tudhaliya IV, was the last strong Hittite king able to keep the Assyrians out of the Hittite heartland to some degree at least, though he too lost much territory to them, and was heavily defeated by Tukulti-Ninurta I of Assyria in the Battle of Nihriya. He even temporarily annexed the island of Cyprus, before that too fell to Assyria. The last king, Šuppiluliuma II also managed to win some victories, including a naval battle against Alashiya off the coast of Cyprus. But the Assyrians, under Ashur-resh-ishi I had by this time annexed much Hittite territory in Asia Minor and Syria, driving out and defeating the Babylonian king Nebuchadnezzar I in the process, who also had eyes on Hittite lands.

The Sea Peoples had already begun their push down the Mediterranean coastline, starting from the Aegean, and continuing all the way to Canaan, founding the state of Philistia – taking Cilicia and Cyprus away from the Hittites en route and cutting off their coveted trade routes. This left the Hittite homelands vulnerable to attack from all directions, and Hattusa was burnt to the ground sometime around 1180 BC following a combined onslaught from new waves of invaders: the Kaskians, Phrygians and Bryges. The Hittite Kingdom thus vanished from historical records, much of the territory being seized by Assyria. Alongside with these attacks, many internal issues also led to the end of the Hittite Kingdom. The end of the kingdom was part of the larger Bronze Age Collapse. A study of tree rings of juniper trees growing in the region showed a change to drier conditions from the 13th century BC into the 12th century BC with drought for three consecutive years in 1198, 1197 and 1196 BC.