The descendants of Jacob had lived in Egypt for more than 450 years, during which time they grew into a nation: the nation of Israel. The Egyptians began to see them as a threat and tightened their control on them, forcing them to work as slaves. In order to escape death, Moses' mother placed him in a basket when he was still a baby and set him adrift on the River Nile. The infant Moses was rescued by the Pharaoh's daughter and brought up in the palace as a royal prince. As an adult, Moses reacted against the unfair treatment of his own people and killed an Egyptian guard. Moses was then forced to flee from the wrath of the Pharaoh. He was driven into exile in the land of Midian. He married Zipporah, the daughter of the Priest of Midian, and worked as a shepherd for forty years. One day, when he was in the desert, Moses heard the voice of God speaking to him through a bush which flamed but did not burn. God asked Moses to lead his people out of slavery in Egypt to the Promised Land.