What was the argument against slavery

There have been arguments over slavery since really the beginning of time, but the most well known was during the early years of the United States (post early colonization). This argument divided the country into two main groups -- the confederation (south) and the federal union (north). The confederates were pro-slavery, whereas the union was essentially opposed to slavery. This whole ordeal led to the secession of many southern cotton states, which sparked the beginning of the Civil War.

The south wanted to continue using slaves to better their strict agriculture economy. For example, their argument was the cotton, tobacco, and rice economy would fail, inevitably  leaving the south in the dust. 

The North, on the other hand, was opposed to the idea of slavery. Although it was not a moral-based idea, the union wanted to better the technological institutions that the south had yet to begin developing. The union wanted to better the economical and political aspects of their "nation".