The most important effect of the Nullification Crisis was that it demonstrated to ultras in the South that nullification would not be a viable way to exert their will on national politics in the future. The issue that caused the event was the passage of a series of protective tariffs that were deemed injurious to Southerners planters, but historian William Freehling showed almost 50 years ago that what really underlay tariff concerns were anxieties about slavery, particularly in light of increased abolitionist agitation in the North. They feared, as Freehling clearly showed in the internal debates over nullification in South Carolina, that the new tariff might set a precedent for federal action against slavery.
After South Carolina backed down from their extreme position, it became obvious that nullification was essentially a dead letter. Southern radicals, particularly those in South Carolina, came to believe that only the threat of secession would be an effective political tool in the future.
The Nullification Crisis was majorly an issue between the southern states especially the state of Carolina versus the Northern states. This was because the tariffs passed by the federal government seemed to work for the North against the South. The South being a consortium of agriculturally based states was going to suffer since the tariffs favoured the manufacturing states of the North with regards to their products. At the risk of war, leaders in Carolina pushed the agenda of nullification and secession of the Southern states. A compromise was reached between the government and the state of Carolina that averted the gridlock.
The issue of "state rights" was not fully dealt with at this point and morphed into a serious altercation between the states and the federal government that eventually led to the American civil war of 1861. As mentioned by rrteacher the Southern states tried to defend their slave policies because their plantations heavily relied on the slaves but the federal government under president Abraham Lincoln was bent on freeing the slaves. The Southern states decided to secede and form the Confederate States of America this was viciously opposed by the Union (United States) leading to the civil war that ended after the Confederacy was vanquished. This can be considered as the major impact of the Nullification Crisis on the United States.