In Across Five Aprils, why did the Creighton family have it hard?

In Across Five Aprils, the Creighton family lives in the midst of the Civil War. The older boys disagree about the war and fight on different sides, Mr. Creighton suffers a heart attack and dies, leaving the family without a father. Jethro is forced to grow up and take over as the man of the house, taking care of and protecting his mother and sisters.