The North (called America) went to war to end slavery, as Lincoln was from the Republican Party that was founded to end it in 1840. The South had keep cheating, breaking Acts of congress, called euphemistically “compromises” so they could get two senators and make the state a slave state. That’s why they broke the Missouri “compromise” and successfully took it over in 1820, installing slavery. That’s why they invaded Kansas with guns in 1850 by taking the guns from the MIssouri armory and crossing the states, as hired “ruffians” who shot and killed the white abolitionists who returned fire. One of those “Northerner” soldiers couldn’t take it any more when and returned from the fighting in Kansas, from the fighting where the “shot heard around America” had already been fired. His name was John Brown, and he got the idea to “return fire” by using the Democratic Party tactic (then the party of white supremacy “planters”): raid the armory and go and attack them back.
The “bleeding” Kansas “incident” was the real start of the Civil War, and everyone said so and was fired up. Senator Charles Sumner then made the famous “Crime Against Kansas” speech, published and passed around up North where people cheered. He called the president an Usurper and many horrific names, accused the Southern Democrats of cheating by laying out solid and thorough arguments and evidence against the stealing of Missouri; accused them of cheating in Kansas and breaking an act of Congress; bringing weapons to kill and intimidate voters; use all those surrogates crossing into Kansas from the South as illegally voting, cheating at the polls to vote for Kansas as a slave state, and calling the president several vicious, nasty names basic saying he was a traitor, saying that the People were turning against all those like president and senators and ruffians “through whose the Assassins and Thugs have derived disgraceful immunity.” Yes, he labeled the political opposition of pro-slavery planters who funded the Kansas cheating and insurrection as “Thugs” and “Assassins.” That would be the equivalent today of some leading white male Democratic Senator of calling Trump that openly on the floor of the Senate (Schumer?, yeah, I can’t think of one either making a detailed power speech lasting for hours railing against Trump).
He ended his speech (you can buy it on Amazon), by urging voters to “turn from every man, whether President, or Senator, of Representative, what’s has been engaged in the Crime” of stealing Kansas by militia invasion supported by the Democratic rich planter class who owned the slaves and the wealth. After his powerful pro-abolitionist speech calling out his cheating and lying colleagues to their face on the floor of the US Senate, Senator Sumner got his head bashed in by the Senator from South Carolina—literally bashed in and almost died. Lincoln then rejected any other compromise with the Southern Democrats, and later gave Sumner a special position during the Civil War when he recovered from his debilitating beating. Sumner was recognized as a hero from standing up so bravely and forcefully against the Southern Democratic Party cheaters, bullies and insurrectionists. Name any one taking such a brave public and open stand today. No one.