Final answer:
The United States fought to bring the South back into the Union to preserve the nation's unity, uphold constitutional principles, and confront the moral issues surrounding slavery. The attack on Fort Sumter rallied the North, and despite the complexity of motivations, including loyalty and a perceived defense of freedom, it became a contest of ideals between federal authority and states' rights.
Step-by-step explanation:
The question of why the United States should fight to bring the South back into the Union after the Civil War touches on complex historical and ethical considerations. The decision to fight stemmed from a desire to preserve the Union, uphold the Constitution, and later, to end the institution of slavery. While some in the North initially preferred a more conciliatory approach, the attack on Fort Sumter galvanized the Union cause. Moreover, the South's secession raised critical questions about the nature of American democracy and whether states had the right to break away from a national government.
After the war, during Reconstruction, opinions varied widely. The assassination of President Lincoln thwarted the chance for a comprehensive plan, leading to debates over whether to punish the South or heal the nation. The eventual military effort to bring the South back was due in part to the fundamental belief that a divided nation could not stand and that all states must adhere to federal authority. This ideological battle, coupled with moral arguments over the wrongs of slavery, fueled the determination to reunite the country.
Understanding why ordinary Southerners, many of whom owned no slaves, were willing to fight and potentially die for the Confederate cause can shed light on the dynamics of civil wars. Historians like James McPherson suggest soldiers fought for their cause and comrades, driven by a sense of loyalty and the belief they were upholding their way of life, liberty, and American values, despite the fact that the war and its underlying issues of slavery and state's rights were more beneficial to the Southern elite.