Slavery has always been a hotly debated topic among Historians, and yet it is often agreed to be a leading cause in the secession of Southern states, and the subsequent Civil War that followed. Spicer said that "the causes of the American Civil War can perhaps be linked to one particular issue – that of slavery" and I would tend to agree with him. The North and the South felt very differently about Slavery and this meant that there were disputes in the very fabric of the American Union; disputes that caused more problems than the different economic climates of the two sides, or the eventual secession of South Carolina, the states that followed it, and the American Civil War.
It is easy to argue that slavery was the cause of the first violent outbursts from each side; John Brown led the raids on Harpers Ferry in 1859 which aimed to free slaves in Virginia. However the famed Southern General Robert. E. Lee arrived and captured Brown, killing 10 of his raiders, but this was starting to emphasise the differences between the North and the South. Southerners began to see all Northerners as violent abolitionists, whilst in reality many Northerners were reviled by Brown's actions and did their best not to associate with him.
This occurred alongside what is now known as "Bleeding Kansas", a huge influx of populace from both the North and the South in order to swing the Popular Sovereignty vote in their favour. The Kansas - Nebraska Act in 1854 meant that each new state would vote on whether they would be a slave state or a free state and so both sides tried to have their way. This ended in violence, and whilst only one man was killed, shops were looted and houses burned. The fact that both sides were always so close to violence over the issue of slavery suggests that it was a hugely important factor in the causation of the American Civil War.
However there are counter arguments to this; the majority of the populations were not involved in such violence, and often slavery was irrelevant to them, as only the rich were able to afford to look after and house the slaves. Moreover the North and the South were split politically, with the Democrats in the South believing in expanding west, an idea known as "Manifest Destiny". The Republicans in the North however held a strong belief in "free labour, free land, free men" (their 1856 slogan). Even there though you can see the effects of slavery, "free labour" and "free men" both point towards the attitudes to slavery, and often political conflicts were born out of the issue of slavery.
Ultimately, it is undeniable that slavery played a large part in the causation of the American Civil. Politically the North and the South differed greatly on their views, and so whoever came into power would anger the other side through their policies. This lead to violence with John Brown and Bleeding Kansas, and tensions eventually culminated in a Civil War.