Americas Role in WWI Discussion

I need an explanation for this History question to help me study. Readings:     1) Wheeler and Becker, Chapter 5, “Homogenizing a Pluralistic Culture:  Propaganda During World War I” Answer the following questions:1) Why did America enter World War I? Generate a list of as many reasons American entered the war as you can think. Why did the United States side with the Allied Powers and not the Central Powers? 2) Who were the Allied Powers and who were the Central Powers?