Volunteers in the Union Army were motivated to commit to military service due to a variety of reasons, including support for abolition on moral grounds, but also economic self-interest. For instance, many recent Scandinavian immigrants were small farmers and saw slavery as a threat to their economic well-being, allowing Southern plantations to outproduce their own operations, which relied on wage labor. As well, factory workers in the North felt their own livelihood was under threat in the event of a Confederate victory, due to the possibility of the future introduction of slaves in industrial production.
Reasons for Southern volunteerism were just as varied and included a patriotic attachment to home states and the perception that they were under threat from advancing Union forces. In the case of African American volunteers, specifically, they were inspired to serve in the CSA Army by a promise of emancipation offered by the Confederate government.
The conflict was not limited to the military realm but impacted civilian life as well. Sherman's "March to the Sea," for instance, laid waste to vast swaths of Southern territory.
Beyond its superior resources and numbers, the North had the benefit of an established government, which gave it greater efficiency in operation. It also had greater domestic support; while the South monopolized a portion of the nation's slave states, the North included all free states plus four slave states. Finally, Northern railroad networks offered the North increased infrastructure for the rapid movement of men and material.