The New Kingdom pharaohs established a period of unprecedented prosperity by securing their borders and strengthening diplomatic ties with their neighbours, including the Mitanni Empire, Assyria, and Canaan. Military campaigns waged under Tuthmosis I and his grandson Tuthmosis III extended the influence of the pharaohs to the largest empire Egypt had ever seen. Between their reigns, Hatshepsut generally promoted peace and restored trade routes lost during the Hyksos occupation, as well as expanding to new regions. When Tuthmosis III died in 1425 BC, Egypt had an empire extending from Niya in north west Syria to the fourth waterfall of the Nile in Nubia, cementing loyalties and opening access to critical imports such as bronze and wood.
The New Kingdom pharaohs began a large-scale building campaign to promote the god Amun, whose growing cult was based in Karnak. They also constructed monuments to glorify their own achievements, both real and imagined. The Karnak temple is the largest Egyptian temple ever built. The pharaoh Hatshepsut used such hyperbole and grandeur during her reign of almost twenty-two years. Her reign was very successful, marked by an extended period of peace and wealth-building, trading expeditions to Punt, restoration of foreign trade networks, and great building projects, including an elegant mortuary temple that rivaled the Greek architecture of a thousand years later, a colossal pair of obelisks, and a chapel at Karnak. Despite her achievements, Amenhotep II, the heir to Hatshepsut's nephew-stepson Tuthmosis III, sought to erase her legacy near the end of his father's reign and throughout his, touting many of her accomplishments as his. He also tried to change many established traditions that had developed over the centuries, which some suggest was a futile attempt to prevent other women from becoming pharaoh and to curb their influence in the kingdom.
Around 1350 BC, the stability of the New Kingdom seemed threatened further when Amenhotep IV ascended the throne and instituted a series of radical and chaotic reforms. Changing his name to Akhenaten, he touted the previously obscure sun deity Aten as the supreme deity, suppressed the worship of most other deities, and attacked the power of the temple that had become dominated by the priests of Amun in Thebes, whom he saw as corrupt. Moving the capital to the new city of Akhetaten (modern-day Amarna), Akhenaten turned a deaf ear to events in the Near East (where the Hittites, Mitanni, and Assyrians were vying for control). He was devoted to his new religion and artistic style. After his death, the cult of the Aten was quickly abandoned, the priests of Amun soon regained power and returned the capital to Thebes. Under their influence the subsequent pharaohs Tutankhamun, Ay, and Horemheb worked to erase all mention of Akhenaten's heresy, now known as the Amarna Period.
Around 1279 BC, Ramesses II, also known as Ramesses the Great, ascended the throne, and went on to build more temples, erect more statues and obelisks, and sire more children than any other pharaoh in history. A bold military leader, Ramesses II led his army against the Hittites in the Battle of Kadesh (in modern Syria) and, after fighting to a stalemate, finally agreed to the first recorded peace treaty, around 1258 BC. With both the Egyptians and Hittite Empire proving unable to gain the upper hand over one another, and both powers also fearful of the expanding Middle Assyrian Empire, Egypt withdrew from much of the Near East. The Hittites were thus left to compete unsuccessfully with the powerful Assyrians and the newly arrived Phrygians.
Egypt's wealth, however, made it a tempting target for invasion, particularly by the Libyan Berbers to the west, and the Sea Peoples, a conjectured confederation of seafarers from the Aegean Sea. Initially, the military was able to repel these invasions, but Egypt eventually lost control of its remaining territories in southern Canaan, much of it falling to the Assyrians. The effects of external threats were exacerbated by internal problems such as corruption, tomb robbery, and civil unrest. After regaining their power, the high priests at the temple of Amun in Thebes accumulated vast tracts of land and wealth, and their expanded power splintered the country during the Third Intermediate Period.