Why were the Egyptians afraid of the Israelites in Egypt?
The Egyptians feared the Israelites because their population was multiplying rapidly and becoming more numerous and mightier than the native Egyptians. Pharaoh worried they might join Egypt's enemies in war and fight against Egypt, so he sought to deal wisely with them and remove them from the land.
Les explains that a new pharaoh arose who knew not Joseph, and he told his people the children of Israel were more and mightier than they. The Egyptians felt defensive because these outsiders were not part of their stock, yet they were multiplying so fast they were outnumbering the natives. Pharaoh and the Egyptian people worried that the Israelites, with increasing numbers, would overtake them, especially since in antiquities it did not take much to overthrow a king and set up another. Quoting verse 10, Les notes Pharaoh's fear that in war the Israelites would join Egypt's enemies and fight against them, so they wanted to get them up out of the land. He also emphasizes that the people numbered millions, not merely the few thousand depicted in The Ten Commandments.