These events are roughly divided into two periods: the first encompasses the gradual build-up over many decades of the numerous social, economic, and political issues that ultimately contributed to the war's outbreak, and the second encompasses the five-month span following the election of Abraham Lincoln as President of the United States in 1860 and culminating in the capture of Fort Sumter in April 1861.

Among the most polarizing of the underlying issues from which the proximate causes developed was whether the institution of slavery should be retained and even expanded to other territories or whether it should be contained, which would lead to its ultimate extinction.

Initially, seven states seceded: Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and Texas.

After the Confederates attacked and captured Fort Sumter, President Lincoln called for volunteers to march south and suppress the rebellion.

Several small skirmishes and battles as well as bloody riots in St. Louis and Baltimore took place in the early months of the war.