They were battling for independence. Many of soldiers from the South had deep roots in their states. Many felt strongly about guarding their rights and trusted the Union was meddling with their rights.
In any case, the North had more labor and industry. When Generals like Grant, Sheridan and Sherman tagged along, the North changed the tide and won the war.
The fighting spirit of the Southerners stemmed from the fact that they were A: fighting for independence. The same way that the Revolutionary War galvanized the population of the British Colonies in the 1770s, the Southern Secession was viewed as fighting for the Southern way of life.
