What caused the decline of ancient Egyptian civilization? The empire on the Nile river reached the peak of its power, wealth and influence in the New Kingdom period (1550 to 1070 B.C.), during the reigns of iconic pharaohs like Tutankhamun, Thutmose III and Ramses II, who may have been the biblical pharaoh of the Exodus story.

At its height, the Egyptian Empire controlled an expansive territory stretching from modern-day Egypt up through the northern Sinai peninsula and the ancient land of Canaan (which encompasses modern-day Israel, the West Bank and Gaza, Jordan and the southern portions of Syria and Lebanon).

But starting with the murder of Ramses III in 1155 B.C., the once-great Egyptian Empire was slowly brought to its knees by a centuries-long drought, economic crises and opportunistic foreign invaders.

Ramses III ruled Egypt for 31 years and is widely considered the last of the “great” pharaohs. His reign coincided with one of the most turbulent and challenging periods in ancient Mediterranean history, known as the invasion of the “Sea Peoples.”

The precise identity of the Sea Peoples is still unknown, but most scholars believe they were an ethnically diverse band of refugees from the western Mediterranean displaced by drought and famine, who came east looking for new lands to conquer and inhabit. Marauding fleets of Sea Peoples may have attacked Egypt at least twice during the reigns of Merenptah and Ramses III.

In 1177 B.C., Ramses III and the Egyptian navy successfully repelled the second massive Sea Peoples invasion, and the pharaoh memorialized the victory on the walls of his temple and tomb complex in Medinet Habu.

But the celebration was short-lived, says Eric Cline, an archaeologist and historian of the Bronze Age, who wrote 1177 B.C.: The Year Civilization Collapsed. Ramses III was able to fight off the Sea Peoples, but not an assassination plot by a jealous secondary queen in his harem. According to CT scans of Ramses III’s mummy, the pharaoh was stabbed through the neck and murdered in 1155 B.C.

“That was the beginning of the end,” says Cline. “After Rameses III, that’s it. Egypt is never the same again.”

In the 12th century B.C., the entire Mediterranean region went through a cataclysmic event known as the “Bronze Age Collapse.” For the kingdoms that fell to the Sea Peoples—or to other contemporaneous calamities like drought and famine—the collapse was swift and absolute. The Mycenaeans of Greece and the Hittites of Anatolia, for instance, saw their cities, cultures and even written languages essentially wiped out.

In part because Ramses III was able to repel the Sea Peoples, Egypt lasted longer, says Cline. But it eventually fell prey to the same problems afflicting the broader region: a “megadrought” lasting 150 years or more and the disintegration of a once-thriving Mediterranean trade network.

“The international connections that had been so prominent and prevalent during the late Bronze Age are all cut,” says Cline. “In Egypt, the 12th century after Ramses III is marked by food shortages and political infighting, and also a rapid decline in Egypt’s role as a major international power.”

After the death of Ramses III, Egypt was ruled by a string of ineffectual pharaohs also named Ramses. (Ramses XI, who died around 1070 B.C., was the last pharaoh of the New Kingdom.) Archaeological records from this period give clues to why and how Egypt entered such a rapid decline.

For example, the mummy of Ramses V appears to have smallpox scars on his face. While historians can’t be sure if he actually died from smallpox, records indicate that Ramses V and his family were buried in newly dug tombs, and also that there was a six-month moratorium on anyone visiting the Valley of the Kings after the burials.

Some scholars suggest this may have been one of the first disease-inspired isolation orders on record—and a possible sign that Egypt was plagued by a smallpox outbreak at that time.

In addition, during the reigns of Ramses V and Ramses VI, Egypt appears to have lost control of important copper and turquoise mines in the Sinai peninsula, since their names were the last of the Egyptian pharaohs inscribed on the sites. Egypt had probably withdrawn completely from Sinai and Canaan by 1140 B.C., says Cline.

Then, under Ramses IX, who ruled at the end of the 12th century B.C., Egypt was rocked by a string of tomb robberies. The economic conditions were so desperate—and the respect of the pharaoh’s authority so low—that thieves brazenly raided the tombs of fallen pharaohs for gold and treasure.

“It’s a shocking crime, but the reign of Ramses IX is just the beginning of a sustained period of royal tomb robberies,” says Cline. “At one point, during the reign of Ramses XI, they had to move some of the royal mummies for safekeeping.”

After the New Kingdom, Egypt was ruled by a succession of foreign powers, further evidence of its decline as an independent empire.

First came the Libyans, a nomadic people from the western frontier of Egypt, whose influence and culture gradually took over the seats of power. Shoshenq I, a pharaoh of Libyan descent, was the first pharaoh of the 22nd Dynasty, who tried to restore the glory days of Ramses III by invading the kingdoms of Israel and Judah in the 10th century B.C.

Then, in the 8th century B.C., the Nubians or Kushites peacefully claimed the Egyptian throne during a time of political turmoil. A succession of Kushite pharaohs ruled Egypt for nearly a century as the 25th Dynasty before being pushed out by Assyrian invaders.

“Once the Kushite kings took over, that was really the end of Egypt as an independent power,” says Cline. “Then the Assyrians came in, followed by the Persians, the Greeks, the Romans and then Islam. If you're talking about ancient Egypt being a power unto itself and being ruled by Egyptians, it was never the same again.”

Egypt experienced its last gasp of greatness under the Ptolemaic Dynasty (305 to 30 B.C.), a succession of Macedonian Greek pharaohs who ruled Egypt after the death of Alexander the Great. Cleopatra VII is the best-known of the Ptolemaic pharaohs, who constructed a magnificent Hellenistic capital in Alexandria.

When Cleopatra and Marc Antony were defeated by the Roman Emperor Octavian (Augustus) in 30 B.C., Egypt became a province of the Roman Republic, bringing an end to the last of the ancient Egyptian dynasties.