What were the short-term causes of the Civil War?
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.
Not exactly sure what you mean by "short-term", but if I take it to mean the more immediate causes--the match to the gasoline as it were--then Confederate troops under Pierre Gustave Toutant Beauregard firing cannons at Fort Sumter in Charleston Harbor, South Carolina in April of 1861 would be the starting point.
In the months leading up to that battle, not only the election of Abraham Lincoln in November of 1860, but his election with a minority of the vote (40%) and without a single southern vote (his name wasn't on the ballot in ten states) confirmed Southerners worst fears: that the North could dictate to them through their larger population and representatives in Congress.
So they seceded. Keep in mind that the war started in April, and Lincoln's election was in November, so Lincoln was pretty patient while he waited to take office, hoping a new compromise could be reached and crisis averted, but the number of states leaving the Union continued to grow, and with Fort Sumter, there was no turning back.
The short term causes of the Civil War were the election of Abraham Lincoln in 1860 and Lincoln's unwillingness to allow the South to secede.
When Lincoln was elected without any Southern support, the South believed that it would be better off as its own country. Southerners felt that the US government would no longer care about the South's concerns. Therefore, they seceded.
Faced with this, Lincoln could have let them go, thereby avoiding the Civil War. Instead, Lincoln tried to keep the Union together. When (in an attempt to do this) he tried to resupply Fort Sumter in South Carolina, the war began.