Yes. In the interval between his election-win and his inauguration.
No state seceded during the election of 1860. South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas declared its secession from the United States following the November 1860 election of Republican candidate Abraham Lincoln to the U.S. presidency. After the Civil War began in April, Virginia, Arkansas, Tennessee, and North Carolina also declared their secession and joined the Confederacy.
It was before the war. As soon as Lincoln won the Election of 1860, South Carolina called a convention where everyone voted for secession. They claimed that slavery was protected by the Constitution, and Lincoln was likely to prevent the creation of any new slave-states. Other Southern states joined them, and soon the war was on.
a major Union military victory
No. South Carolina seceded on December 20th, 1860, before Lincoln was officially sworn in as President. However, the state did secede as a reaction to Lincoln's election.
A substantial portion of the population in those states were against secession.
Both sides believed that war was imminent. The build up began well before South Carolina seceded and precipitated the attack on Fort Sumter. Both sides were prepared for the consequences of secession.
Lee and Lincoln both felt that secession would damage the country, and allthough there were many contrasting points of view in the nation at the time, they felt that it would be a bad idea to permit any secession.
Led by South Carolina, seven Southern states seceded from the union after Lincoln was elected and before he took office.
In the prelude-months before the formal beginning of the American Civil War, the event that prompted South Carolina to secede from the Union was the election of Abraham Lincoln as the 16th President of the United States. With Lincoln's strong anti-slavery sentiments well-known throughout the nation, South Carolina anticipated further attacks upon its slave-holding way of life; therefore, it chose to secede from the Lincoln-led Union rather than endure these anticipated attacks.
December 1860, as soon as it heard the result of Lincoln's election as President. Incidentally, it did not just attempt to secede. It did secede, followed by ten more Southern states.
President Andrew Jackson supported the preservation of the Union and in response to South Carolina's threat of secession, Jackson ordered armed forces to the South Carolina capital of Charleston to enforce the Tariff Act. The volatile situation was remedied only when Henry Clay negotiated a compromise tariff acceptable to both the federal government and South Carolina. Calhoun ultimately resigned the vice presidency in protest.
The most immediate cause of the South's secession from the union was the election of Lincoln during the 1860 election. The South did not support Lincoln at all (in some southern states, his name didn't even appear on the ballot) and when he won the election they felt unrepresented by the government. South Carolina was the first to go.