The Civil War was based upon strong ideological and political differences during the 19th century. Abraham Lincoln was the Republican president that led the way to changing America.
Lincoln [became] the first Republican president and his election led to Southern secession and the Civil War. A shrewd politician, Lincoln managed to lead the North to victory and laid the foundation for the abolition of slavery...
The conflict was the worst ever fought on American soil, pitting state against state, as well as family members against their relations.
The dissolution of slavery, a highly important wartime goal for many Northern states, was opposed violently by the South, which depended almost exclusively upon slaves to support their financial prosperity.
By the war's end, the casualty count was high (dead were approximately 620,000 soldiers, two percent of US population in 1861), and a great many properties in the South were left in ruins, as was the Southern economy.
...in late 1700s, the states south of the Mason-Dixon line would begin arguing for the perpetuation of slavery in the new United States while those north of line hoped to phase out the ownership of human chattel.
The anger and hatred many felt below the Mason-Dixon line lingered well into the 20th century, and according to several authors such as Tony Horwitz in his book Confederates in the Attic, it still exists in some places today.
The end of the Civil War—and specifically the surrender of the South—changed the trajectory of the US. It is estimated by some that the United States would never have been able to rise up "as the world's largest economy and foremost democracy by the late 19th century" if the South had not been defeated.
The institutions and ideology of a plantation society and a slave system that had dominated half of the country before 1861 went down with a great crash in 1865 and were replaced by the institutions and ideology of free-labor entrepreneurial capitalism. For better or worse, the flames of the Civil War forged the framework of modern America.
The Civil War brought about changes that are still recognizable today.
Slavery was ended with the ratification of the 13th Amendment. In places throughout the country, especially in the South, struggles in the early part of the 20th Century through the Civil Rights Movement of the 1960s, brought about change for African-Americans fighting for equality on every level of American society. Such strides in diversification altered education, employment, politics, etc.
Many cities in the modern day have moved away from (for example) the failing coal or steel industries that once dominated those places. The adoption of new plans for diversified industry have allowed Americans to remain. For example, Pittsburgh, PA, once dependent upon outdated forms of industry, has adapted and excelled in new industries (e.g., solar and wind power). Such was also the case with the South after the war. Without the ability to rely on slave labor, economic diversification was required for the region to recover, survive, and thrive.
Perhaps it is would be prudent to add that battles between segments of the country are generally no longer fought on the ground, but in the government. While families may be split by political opinions or biases, the struggle is no longer one of carnage and bloodshed. That is not to say that everything is perfect now: in some ways, the battle continues. And the American people search for answers to problems that many believe may still remain from the time of the US Civil War.