This is actually a trick question, because there were two leaders during the American civil war, Jefferson Davis and Abraham Lincoln.
Jefferson Davis is the <em>president of the CONFEDERATE STATES OF AMERICA.</em>
So generally,
Abraham Lincoln would be the president of USA.
I believe the answer is C but I could be wrong double check
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States