The reason for Israel's Oppression was that the Israelites honored false gods.They sinned agains the First Commandment which states:
I am the Lord thy God, who brought thee out of the land of Egypt, out of the house of bondage. Thou shalt not have strange gods before me. Thou shalt not make to thyself a graven thing, nor the likeness of anything that is in heaven above, or in the earth beneath, nor of those things that are in the waters under the earth. Thou shalt not adore them, nor serve them: I am the Lord thy God, mighty, jealous, visiting the iniquity of the fathers upon the children, unto the third and fourth generation of them that hate me; and showing mercy unto thousands to them that love me, and keep my commandments.
Exodus 20:2-6
They were specifically told, "I am the Lord your God; do not worship the gods of the Amorites, in whose land you live." They did not heed this warning and were forced to pay the concequences because of it.
Today, many of us are like the Israelites. We put "things" before Him. We worry more about driving a fine car, living in a home filled with finery, making gobs of money, than we do about worshiping and honoring God. In effect, we worship false gods... wealth, fame and material goods.