A lot of events happened that led up to the Civil War! I would probably say that the biggest ones were the Missouri Compromise (Thomas Jefferson wrote that it was like grabbing a wolf by its ears), sectionalism (when people are more loyal to their state than their country), the annexation of new states, and the idea of States' Rights.
Slavery was often called a "peculiar institution" because of the controversy of the trade. Many from the North and South (mostly small farmers that depended on the slave-owning plantation farmers) were appalled at the idea that people were being enslaved and forced to work in grueling conditions. Others believed that slavery was necessary for the production of raw materials, and it has to stay for the benefit of the economy. Lots of clashes came from this, but mostly it was the argument of states' rights.
Lincoln's Emancipation Proclamation states that all slaves in the Confederate territories were free (but not in the border states, very important). This was incredibly significant because it confirmed that the existence of the war was for the freedom of slaves.
The Battle of Gettysburg was amongst the only battles fought in the Northern territory in the American Civil War. It was the turning point of the war for the North, and it basically defined the winner of the War. Pickett's Charge, along with many other Confederate tactics during the three-day battle proved this.
Although Canada was still a part of the British Empire during the Civil War, Canadians still fought on both sides. At the aftermath of the Civil War, Canadians were concerned for the invasion of the United States into their territory, so it encouraged them to try to gain their own independence. I'm not too sure about this, and I would encourage you to try to find other sources. But I hope this helps!