You will ASSUME THE ROLE of an opponent to war with Mexico, expressing the reasons why the United States would not be justified in going to war.
Also, go to these webpages for info-
http://www.digitalhistory.uh.edu/disp_textbook.cfm?smtid=3&psid=3672
http://umich.edu/~ac213/student_projects06/magsylje/viewpoints.html