Short-term causes of the American Civil War certainly include Lincoln's refusal to meet with the commissioners that were sent by the Confederate government to buy Fort Sumter and other federal property that was located in the Confederacy. This was followed by Lincoln's launching an invasion fleet from New York to invade South Carolina. The Confederacy responded to this by subdueing Fort Sumter so that the invasion fleet could not land.
Upon the election of Lincoln to the Presidency, six southern states seceeded and formed the Confederate States of America. In those days, secession was a Constitutional right, and most citizens of America, both northern and southern, so believed. When Lincoln called for the states of the union to send soldiers to conquor the states that had seceeded, seven more states seceeded. (Two of these states had strong factions that remained loyal to the Union so that both sides claimed them.)
So we have it in order: Lincoln's refusal to sell federal property in the Confederacy, Lincoln's launching of an invasion fleet, and Lincoln's call for troops to suppress Constitutional rights.
But why did Lincoln direct events towards war? If the Republican party and its president had earned the reputation of being the party and the president who presided over the dissolution of the Union, they would never have had a chance of being relected to power.
Much of this is discussed on pages 345-378 of vol. II of A Constitutional View of the War Between the States by Alexander H. Stephens (ca. 1870). This book is still admired by American Constitutional scholars.