I supposed the best evidence that the Civil War brought the United States together is that we have never had another civil war since then and we have never had any serious talk of any state or states secedeing.
The Civil War brought the US together in two ways:
- It ended slavery. Since slavery was a major bone of contention between the two regions, ending it helped make the US more of a united whole.
- It ended the idea that states could secede. Up until that time, some people believed states had the right to leave the Union whenever they wanted. Hardly anyone thinks that anymore.
So we are a more united nation now than we were back then, and the Civil War is part of the reason for that.
Perhaps something else we should consider with how the civil war brought our country together is to think about the fact that regardless of state allegiance, we eventually placed more focus on country. As someone earlier posted the United States is. In addition, it perhaps made our political leaders more wary of the diverse political opinions held by those in our country, and now the work harder to garner and retain the favor of our United States Citizens.
I would agree with other posters that the greatest evidence is the fact that we have not had another civil war since then. You look at other countries that have multiple civil wars or attempts at civil uprising. The United States has been able to avoid that.
The Civil War was one of the last times we saw the majority of people in the country refer to their states as their countries. Their loyalty used to be to Virginia, or Massachusetts or Texas. We see very little of that today, and much more patriotism towards America as a whole.
The war ended legal slavery - for the first time, all American states followed the same law as regards slavery. Sure racism, discrimination and sharecropping made it like slavery, but it was progress.
The War to Prevent Southern Independence did bring America together, though not at once. Before the War, there were two dominant and competing social systems in the US: industrialism and seigneurialism (Seigneurs derived their wealth from use of the land, such as plantation agriculture and livestock grazing). Each system was dominated by a wealthy class of men; under each system, the middle class and the masses who were dependent upon that system, developed social and political views which were compatible with it; that is to say, each system influenced the views of the people who lived under it.)
The War destroyed seigneurialsim and gave industrialism exclusive hegemony. Under industrialism, tax structures, laws and business regulations have gradually evolved to limit farming to only so much as is necessary to support industrialism, with all farmers excess to that need forced out of business and into the ranks of factory labor. (The more laborers seeking a job in a factory, the lower the wages that must be paid by the industrialists.) It is now so difficult for someone to have a farm just for the support of his own family and for a place for his children to grow up, that almost no one does this anymore in the US, and millions of acres of US farm land are sitting idle. Thus, Americans all over the US are more alike in that more of them in every section work in factories.
And the middle class occupations (such as bank managers, lawyers, engineers) that support whatever social system is hegemonic, are now influenced by only one social system, industrialism, so that members of the middle class all over the US are made more alike in their social and political views.
It didn't...at least not right away. When General Lee surrendered to General Grant at Appomattox Court House in April 1865 the Civil War officially ended and the union was restored. However, your question is not as simple as it appears. The political, social, and economic divisions between the north and south prior, during, and after were liken to a cut that might heal but quickly festered into a wound whose future was uncertain. Here's why;
1. Lincoln's plan was based upon 'malice towards none', establish new governments and take an oath of loyality to the union...however after Lincoln was assassinated there were those in Congress that believed that the pre-war southern white leaders would regain power instituting the segregationist 'Black Codes' depriving civil rights for the African Americans.
2. After two years the U.S. Congress passed The Military Reconstruction Plan of 1867 it included: U.S. military control of the south until new southern state governments, every state had to ratifity the 13th,14th and 15th Amendments...all sounds good right???
3. Southern state governments instituted procedures to restrict the political power of African Americans. For example, poll taxes were assessed African Americans who wanted to vote. (Sharecropping did not exactly leave the newly freed slave extra money) Another tactic were the Literacy tests, where by African American voters were asked to answer several questions about U.S. history. It must be noted that there were plenty of white illiterate people in the south at this time, however the Grandfather clause exempted literacy tests from white people if their grandfathers' were eligible to vote before the war.
4. As a result the era of 'Jim Crow' was born. Custom in the new south became 'de jure segregation' and it became southern state law into the 20th century.
5. 100 years later the U.S. Congress passed the 'Voting Rights Act of 1965' to reaffirm the meaning and hopefully the legacy of 'All men are created equal' and 'We The People'.
6. The Civil War forced Americans on both sides to reconcile their belief (if any) in humanity...and if the Civil War accomplished anything it was the nation's transformation from:
'The United States 'are' to 'The United States 'is'
The Civil War brought the country together, because it sent a strong message that unity is worth fighting for and even dying for. More importantly, the North won. This point is important to emphasize, because the North did not allow any states to secede. If the South won, things may have had a very different outcome. So, it is probably more proper to say that victory of the North in the Civil War (and not just the Civil War) brought America together. Also we should point out that the Civil War was a strong force in the ending of slavery.
One of the major reasons why the Civil War brought the nation together would be that the intensity of emotions might have been spent given the arduous and brutal nature of the conflict. Both sides were fairly well spent at the conclusion of the war. To a large extent, both sides wanted to move on from the conflict. Northern industrialists were working with former Southern plantation owners in order to develop new streams of revenue in the South. At the same time, the idea of Reconstruction was intended to bring together both sides together in a more unified nation. One could also suggest that the Civil War brought the nation together because there has not been another conflict on the same level since.