The war was a waste of people. Primarily young men, not Northern leaders or northern businessmen. Machinery and industrialization was going to cause the South to give up on slavery in a few years anyway. The North claimed to be great liberators of slavery, but in reality the changes were not that significant for a long time. Slaves became sharecroppers who had similar lifestyles. The sharecroppers lived in overt poverty until machinery and industrialization started to replace them. Even then, their families continued to live in poverty for the most part.
Yippie, the North "abolished" slavery but there were no jobs for the ex-slaves. If the North really cared about slaves, they would have forced some rules for how slaves were treated onto the South years before it came to a War.
The Union could have made slavery illegal in the Northern states, made it illegal to import slaves in all areas and then they could have slowly purchased slaves from the South until the supply dwindled to the point that the South could no longer rely on them. It was the dumbest war in the history of wars and completely unnecessary.
The real motivation was not even slavery. They used slavery as an excuse to do what they wanted to do which was to be in control of the south and to take the natural resources that were there without having to deal on the South's terms.
The North (Union) was basically doing the same thing the Mongols, Romans, Crusaders and others had done and what Hitler would later do. They wanted to be in charge of other people. The South wanted to be the owners of slaves. The North wanted to be the owners of the South. If you don't believe that, look up the history of Carpetbaggers. Hint, they were Northerners that came to the South after the war for person gain.
Was the Northern regime so incompetent they could not enforce any changes on the South over time using the processes available?
Here is one example of the real reasons behind the war:
Historically, southern slave-holding states, because of their low cost manual labor, had little perceived need for mechanization, and supported having the right to sell cotton and purchase manufactured goods from any nation. Northern states, which had heavily invested in their still-nascent manufacturing, could not compete with the full-fledged industries of Europe in offering high prices for cotton imported from the South and low prices for manufactured exports in return. Thus, northern manufacturing interests supported tariffs and protectionism while southern planters demanded free trade.
The above issue was about money and control. The North wanted more money but the South resisted changes that would result in more money for the North and less for the South.
The Northern leaders and Northern businessmen wanted more power and money. They could care less about the slaves. Slavery was just their excuse for the war. They caused the following to happen in order to enrich and further empower themselves:
North:
110,000+ killed in action/died of wounds
230,000+ accident/disease deaths
25,000–30,000 died in Confederate prisons
365,000+ total dead, 282,000+ wounded
181,193 captured
Total: 828,000+ casualties
South:
94,000+ killed in action/died of wounds
26,000–31,000 died in Union prisons
290,000+ total dead
137,000+ wounded
436,658 captured
Total: 864,000+ casualties