The prevailing theory regarding the origin of the Hyksos is that they were a nomadic Asiatic/Indo-Aryan people that had begun emigrating southward from the Caucasus Mountains around 2000BCE. Along their journey to the south, various splinters of this larger group would opt to settle or to head in a different direction. These splinter groups would go on to form the basis for such early bronze age civilizations as the Hurrians, Mitanni, Hittites and Kassites.

Written references to Hyksos people in Egypt precede their "invasion" by several centuries, though the term's rather sweeping definition of "rulers of foreign lands" makes it difficult to distinguish between the actual Hyksos and other foreign groups such as the Phoenecians. It is still fair to assume that the Hyksos didn't simply appear en masse one morning, hitherto sight unseen. More than likely, they had been slowly appearing and working their way into Egyptian society for decades. Around the year 1730BCE, either the bulk of the Hyksos people or some sort of organized Hyksos army appears to reach Egyptian territory in the Sinai Peninsula and began methodically heading south and west.

Unfortunately for the Egyptians, the Hyksos had three rather massive military advantages:

1. The composite bow.
2. The horse-drawn chariot.
3. Iron weapons and early body armor.

Imagine, if you will, how a battle between the Hyksos and Egyptians would have unfolded. The Hyksos would likely fire on the Egyptians with chariot-mounted archers while the Egyptians' primitive bows were still out of range, simply retreat several hundred yards whenever the Egyptians got too close for comfort, then begin firing anew once safely out of range once again. Assuming the Egyptians made some sort of mad dash for the Hyksos battle lines and managed to make it into melee combat, their bronze weapons would bounce off the Hyksos' early version of chainmail shortly before they got a very personal taste of modern warfare courtesy of a Hyksos soldier's iron mace. If, through overwhelming numbers alone, the Egyptians were able to overrun the Hyksos forces, the Hyksos could simply get on their chariots and retreat or regroup at a speed the Egyptians couldn't even match.

I haven't even mentioned flanking yet.

Given these incredible military advantages, the fact that the Hyksos didn't run roughshod over the entirety of Egypt seems to indicate that their intentions weren't outright hostile. If they'd wanted to take Egypt lock, stock and barrel, it seems very likely that they had the ability to do so. Instead, they were content to settle in the Nile Delta and let the rest of Egypt pay tribute to them as their nominal rulers.