arose over Egypt

Here "Egypt" refers to the people of Egypt. AT: "began to rule over the people of Egypt" (See: rc://en/ta/man/translate/figs-metonymy)

He said to his people

"The king said to his people"

These were the people who lived in Egypt, the Egyptians.

The word "us" is inclusive and refers to the king and his people, the Egyptians. (See: rc://en/ta/man/translate/figs-inclusive)

Here war is spoken of as a person that is able to act. (See: rc://en/ta/man/translate/figs-personification)

"leave Egypt"