A nicely written summary of the attack on Fort Sumter can be found on the Smithsonian’s page called “The Civil War Begins”

In December 1860, a little more than a month after Lincoln’s election, South Carolina’s secession convention, held in Charleston, called on the South to join “a great Slaveholding Confederacy, stretching its arms over a territory larger than any power in Europe possesses.” […] According to historian Douglas R. Egerton, author of Year of Meteors: Stephen Douglas, Abraham Lincoln, and the Election that Brought on the Civil War, “To win over the yeoman farmers—who would wind up doing nearly all the fighting—the Fire-eaters relentlessly played on race, warning them that, unless they supported secession, within ten years or less their children would be the slaves of Negroes.” […] Militiamen itching for a fight flooded into Charleston from the surrounding countryside. There would soon be more than 3,000 of them facing Fort Sumter, commanded by the preening and punctilious Pierre Gustave Toutant Beauregard, who had resigned his position as West Point’s superintendent to offer his services to the Confederacy.

This explanation of the war-mongering blood-thirsty slaveholders contrasts heavily with the description of calm and professional soldiers finding themselves surrounded by hostile enemies of America.

With communications from his superiors reaching him only sporadically, Anderson was entrusted with heavy responsibilities. Although Kentucky born and bred, his loyalty to the Union was unshakeable. In the months to come, his second-in-command, Capt. Abner Doubleday—a New York abolitionist, and the man who was long credited, incorrectly, with inventing baseball—would express frustration at Anderson’s “inaction.” “I have no doubt he thought he was rendering a real service to the country,” Doubleday later wrote. “He knew the first shot fired by us would light the flames of a civil war that would convulse the world, and tried to put off the evil day as long as possible. Yet a better analysis of the situation might have taught him that the contest had already commenced and could no longer be avoided.” But Anderson was a good choice for the role that befell him. “He was both a seasoned soldier and a diplomat,” says Hatcher. “He would do just about anything he could to avoid war. He showed tremendous restraint.”

After some negotiation and brinkmanship, the Confederates fail patience and begin the Civil War with America.

In the early hours of April 12, approximately nine hours after the Confederates had first asked Anderson to evacuate Fort Sumter, the envoys were again rowed [by their slaves] out to the garrison. They made an offer: if Anderson would state when he and his men intended to quit the fort, the Confederates would hold their fire. Anderson called a council of his officers: How long could they hold out? Five days at most, he was told, which meant three days with virtually no food. Although the men had managed to mount about 45 cannon, in addition to the original 15, not all of those could be trained on Confederate positions. Even so, every man at the table voted to reject immediate surrender to the Confederates.

The pride of these Americans surrounded and heavily outnumbered and outgunned, refusing to surrender, enraged the Confederates who responded by announcing they soon would begin war. Aiming for the American flag they managed to knock it down only to find it would be raised again, as the Americans defended their country valiantly for days.