In terms of the legislative acts and initiatives you referred to, it is important to note their relevance and how they are connected. The Wilmot Proviso (1846) was a proposal that the United States Congress ban slavery in the territory acquired from Mexico as a result of the Mexican-American War. This proposal ultimately failed, yet it was one of the major initiatives that lead to the Civil War. Four years later, the Compromise of 1850 banned slavery in Washington DC. However, included in this set of legislation was the Fugitive Slave Act, meant to pacify Southern slave-owners by allowing them to track down runaway slaves. Southerners were still not satisfied by the act, believing it would not be effective in the long run and still fearing the threat of slave uprisings.

The subsequent Kansas-Nebraska Act was the most significant influence precluding the Civil War. The Lecompton Constitution of 1857 was also a major influence on the war: the proposed legislation aimed at preserving slavery in the state of Kansas, which resulted in a national controversy that further split the country.

To address your final question as well as the element of morality influencing the war, the Union was not particularly motivated to abolish slavery in the early years of the civil war. Rather, the focus was on keeping the country together. There was a clear anti-slavery sentiment in the Northern States, but wartime conditions influenced the objective of abolition in the war's final years. As the South achieved decisive victories, military necessity furthered support for abolition. By the end of the war, approximately 179,000 black men fought on the Union side, making up 10% of the Union Army. Moreover, anti-slavery views also strengthened as many African Americans fled enslavement through self-emancipation.