From about 1800 BCE people from the Levant, attracted by the fertile lands and the prospect of jobs in engineering, slowly infiltrated the Nile delta, trading and settling.
About 80 years later they were powerful enough to set up a semi-independent vassal state in the eastern Nile delta with their capital at Avaris.
The native dynasties were weakened, possibly by famine or plague, unable to stop them.
Egyptians and foreigners lived side by side until around 1650 BCE both were invaded by the Hyksos, who probably also originated from the Levant.
The newcomers quickly gained control of Lower Egypt and set up their own Egyptian dynasty, the 15th.
Egypt had traditionally relied mostly upon its borders to defend itself.
The Mediterranean in the north, the Libyan desert in the west, fortresses in the south and Red Sea plus Sinai desert in the east
had for a long time deterred almost all attackers except for occasional raiding nomads.
But these were no defense against the steady immigration, though at first there was no war at all, not even strife.
The Hyksos expanded the edge of their influence slowly yet steadily southward, taking Memphis in 1674 BCE and even Thebes in 1582 BCE, though they lost that city three years later.
Their expansion reversed the original situation, where the north payed tribute to the south.
Now the south had to pay tribute to the north, though it remained politically independent.
It is not clear how much the advance was supported by migration or war, by numbers or military superiority.
All this did not go well with the rulers of Upper Egypt, who around 1560 BCE started a counteroffensive under pharaoh Seqenenre Tao.
The Egyptians modernized their army and adopted the same weapons and tactics as their enemies.
Then they speedily, in about 30 years, pushed back the Hyksos.
Finally Ahmose, founder of the 18th dynasty, managed to expel them, reuniting Egypt.
Again it is not clear how much this victory is to be attributed to military innovation, political and religious unity or troubles in the north (possibly again plague).
Warfare in Egypt always concentrates on the Nile valley.
There is no room for outflanking manoeuvers, except at the Faiyum oasis and in the triangle-shaped delta.
The Nile offers good opportunities for transport over water, but historically lacked large fortresses, except in the south.
This meant that when a defensive position was broken, attackers could quickly advance and make lots of progress.
This is probably why, despite running up for about 30 years, the final campaign of Ahmose was completed in a single year.
The struggle between Egyptians and Hyksos is echoed in Egyptian myth.
The Hyksos, while staying in Egypts, adopted much of Egyptian lifestyle and associated themselves with the god Seth, whom they called Sutekh.
Seth, who had up to that point been an ancient god of desert, war and Upper Egypt, in the eyes of the southerners became associated with evil.
Mythology tells us how he killed Osiris, who was then resurrected by his wife Isis and avenged by his son Horus, who of course was linked to Thebes.
The Hyksos brought several innovations to the always conservative Egypt,
including the chariot, composite bow,
advanced techniques for farming, bronze working and fortification.
These were adopted by the Egyptians and transformed their state from isolationist to imperialistic.
During the New Kingdom, Egypt fought several wars in the Levant, shifting its border with states like Mitanni and Assyria back and forth.
War Matrix - Invasion of the Hyksos
Late Bronze Age 1600 BCE - 1100 BCE, Wars and campaigns