It started because Lincoln had won the 1860 election on a ticket of no new slave-states, so the South was doomed to be outvoted in Congress, which would pass laws that favoured the North at the expense of the South. So most of the slave-states broke away to form the Confederate States of America.
As for when it started, there was no actual declaration of war. The Confederacy could claim that it didn't want a war at all; it just wanted to defend its borders. Lincoln could not declare war on the Confederacy, because Congress did not recognise it as a sovereign nation.
The first shots were fired by the Confederates at the US Army garrison on the island of Fort Sumter in Charleston harbour on April 12th 1861, and Lincoln called for volunteer troops. The war was on.
It means usually calm, cheerful: not easily angered or upset
Slavery, different views of how a government should be run, states rights, peer in the Senate, and politics
Christianity is the most widely practiced in europe
