From 1861 to 1865, the United States was ripped in two by war – with the Union in the North and the seceded states, the Confederacy, in the South. These four years witnessed unprecedented bloodshed, the rise and fall of perhaps America's greatest president, Abraham Lincoln, and the eventual abolition of slavery. The Civil War has helped define America ever since, and names like Gettysburg, Antietam, Lincoln, Robert E Lee and Ulysses S Grant are instantly recognisable.

Click through this gallery to discover lesser-known facts about America’s bloodiest conflict...

It is difficult to accurately calculate the total number of fatalities during the Civil War, but for many years the standard figure was 620,000 across both armies. Some newer research, however, has suggested that the death toll was much higher – at around the 750,000 mark. Either way, that's more Americans dead than in World War I (116,000), World War II (420,000) and the Vietnam War (58,000) combined.

Yet by far the biggest killer was not fighting, but disease. Around two-thirds of the total deaths were caused by illnesses like dysentery, pneumonia, typhoid and malaria.

Civil War generals did not stand behind the battle watching on, but were often in the thick of the action. This is typified by the renowned Confederate general Thomas 'Stonewall' Jackson holding the line at the First Battle of Bull Run in 1861. Leading from (or at least near) the front, however, made these men appealing targets, and generals had a similar chance of dying to the rank and file.

Of the 426 commissioned men in the Confederate Army, for example, nearly one-fifth died in battle and around half were wounded. At the extremely bloody Battle of Antietam in 1862, both sides lost three brigadier or major generals, with another six each wounded.

Following the Battle of Shiloh in 1862, physicians tended to the wounded lying in the cold Tennessee mud and noticed something strange on some of their patients: their injuries were emitting an odd greenish-blue glow. What’s more, those exhibiting glow-in-the-dark wounds had a better chance of survival, leading the men to dub the mysterious phenomenon 'Angel’s Glow'.

It was not until the 21st century that an explanation emerged. A bioluminescent bacteria that lives inside microscopic worms could have been rife at Shiloh, and the chemicals they produced helped clean wounds and reduce the risk of infection.

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Considering the death toll that was to come, it is perhaps surprising that the first battle of the war did not result in a single casualty. On 12 April 1861, Confederate forces bombarded the Union-held Fort Sumter at the entrance of Charleston Harbor in South Carolina. The attack lasted 34 hours and ended with the fort’s surrender, but no deaths.

In fact, more dangerous than the battle was the surrender ceremony afterwards. The Union soldiers were permitted to carry out a 100-gun salute as they lowered the American flag, and an accidental explosion killed Private Daniel Hough, the war’s first casualty.

At the start of the war the North had good reason to be confident about their chances, as they had better infrastructure, more resources and a much larger population to call upon. Many, therefore, believed the war would be short and relatively bloodless.

Such was the optimism that at the First Battle of Bull Run in July 1861, civilians from Washington DC, including senators, followed the Union army and found a spot on the hills around the battlefield. They even brought picnics and opera glasses to watch what was sure to be a decisive victory. Instead, the Confederates won the battle, and the observers had to make hasty exits.

When the inventor Christopher Spencer developed a rifle capable of firing an astonishing 20 rounds a minute and offered it to the Union Army, you might assume they would have jumped at the chance. Instead, Union higher-ups worried that the gun would burn through ammunition. To prove the worth of his weapon, Spencer went right to the top, strolling past the White House sentries gun in hand.

Luckily for him, Lincoln was impressed and asked to test the rifle himself, which he did on the National Mall. Not too long afterwards, a big order was put in, and around 100,000 Spencers had been produced by the end of the war.

Since much of the fighting took place in the South, life became very difficult for civilians in the Confederacy. They faced an invasion from Union forces as well as a naval blockade, which cut off supplies. One Christmas morning, a Confederate general named Howell Cobb famously told his children there would be no gifts from Santa Claus because the Yankees from the North had shot him.

But it was in the North that the modern image of Santa was partly created. In an edition of Harper’s Weekly at Christmas 1863, cartoonist Thomas Nast depicted a portly St Nick with a white beard and a sleigh full of presents – and as a supporter of the Union.

The phrase 'brother against brother' is often used to illustrate how, in the Civil War, wearing the blue uniform of the Union or the grey of the Confederacy came down to deeply-rooted political, social and cultural beliefs that divided Americans. For some families, it was literal. Thomas Leonidas Crittenden (pictured) was a Union general, while his brother George earned the same rank for the Confederates.

Brothers James and Alexander Campbell were even on opposite sides of the same battlefield, at Secessionville in 1862, without realising. And after the Battle of Champion Hill in May 1863, Union soldier John McLaughlin found his Confederate brother Henry and took him prisoner.

A new type of vessel developed by the Confederacy secured its place in history as the first submarine to sink an enemy ship in 1864. HL Hunley was nearly 40 feet (12m) long and had a crew of eight, most of whom were needed to work the hand-cranked propeller.

On the night of 17 February, it approached the USS Housatonic, stationed off Charleston Harbor, and rammed it with a spar torpedo (essentially an explosive on the end of a long pole). The ship sank, but so did the Hunley, which was only rediscovered in 1995. The 'successful' attack, therefore, which resulted in five Union deaths, cost the Confederacy eight men.

It is well-known that Confederate sympathiser John Wilkes Booth assassinated President Abraham Lincoln on 14 April 1865. But less than a year earlier, the Lincoln family had reason to praise the Booth name.

While standing on a train platform, Edwin Booth, brother of the assassin, saw a young man fall onto the tracks just as a train was moving off, and managed to pull him to safety. He had just saved Robert Todd Lincoln, the president’s son – not that he knew that. If anything, Robert was the one in awe, as his rescuer (pictured) was one of the most celebrated Shakespearean actors of his day.

On New Years' Day 1863, Abraham Lincoln issued the Emancipation Proclamation, declaring that all slaves in the Confederate states, numbering between three and four million, "shall be then, thenceforward, and forever free". This did not lead to immediate freedom, however, since the proclamation only applied to rebel Confederate states, and there was no chance of freedom in areas under Southern control.

Instead, the proclamation's impact was more to embolden slaves to escape to the North in large numbers. It would not be until the 13th Amendment, passed by Congress in January 1865 and ratified that December, that slavery would be officially abolished.

After the Emancipation Proclamation slaves fled the South, and many enlisted in the Union Army. Around 180,000 Black men served in segregated regiments of the United States Colored Troops, with another 20,000 in the navy. This comprised roughly 10% of Union forces.

Black soldiers were paid $10 a month and were charged for their uniforms, while white soldiers received $13 without extra charge. Congress eventually granted equal pay in 1864. Perhaps the most famous Black soldiers of the war were the 54th Massachusetts, who fought with famous valour at the Second Battle of Fort Wagner in July 1863.

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During the war, an Ohio lawyer and congressman named Clement Vallandigham was one of the leaders of the Copperheads, a faction opposed to the North’s war policy that called for a peace settlement with the South. For his attacks on Lincoln and the government, Vallandigham was arrested and exiled to the Confederacy. When the war ended, he returned to the law in Ohio.

In 1871, while defending a man on trial for murder, Vallandigham suggested that the victim had actually shot himself while taking his pistol out of his pocket. Unfortunately, he accidentally used a loaded gun during his re-enactment of the scene and shot himself. He died, but his client was acquitted.

The top generals of the Union and Confederacy were undoubtedly Ulysses S Grant and Robert E Lee respectively. Both had graduated from the United States Military Academy at West Point, New York, and both served in the Mexican-American War (1846-48). Once the Southern states seceded, Lee sided with the South and became its leading commander, while Grant rose through the Union ranks.

It would be more than three years into the war, however, before they faced off in battle: in the Overland Campaign of May and June 1864. The brutal expedition resulted in around 90,000 deaths, but it proved a major step for the Union in winning the war.

Although the Battle of Gettysburg was the deadliest engagement of the war – with over 50,000 killed, wounded or missing across three days – the single worst day was 17 September 1862, at the Battle of Antietam. The Confederate general Robert E Lee had invaded the North, but he was met by the Army of the Potomac, which managed to stall his advance. It came at a heavy price: in one day, there were a recorded 22,717 casualties from both sides, making it the bloodiest day not only of the war, but of all American history.

Covering 639 acres and the remains of more than 400,000 people, Arlington National Cemetery in Virginia is the most important burial ground for military personnel in America. It all began with the internment of Private William Christman of the 67th Pennsylvania Infantry in 1864.

The Arlington estate had belonged to Mary Custis Lee, the wife of Robert E Lee, but was confiscated by the Union. The decision to turn it into a cemetery was partly to make the site uninhabitable for the Lees were they ever to return. They did not, and their former house, a Greek Revival-style mansion, now serves as the Robert E Lee Memorial.

Albert Henry Woolson was just 14 years old when he followed in his father’s footsteps and signed up for the Union Army in 1864. Serving as a drummer boy and bugler with the 1st Minnesota Heavy Artillery Regiment, he did not see combat and was discharged in September 1865.

Decades later, in the mid-20th century, he and other aging survivors of the war became mini-celebrities. Woolson (pictured) died on 2 August 1956, at the age of 106. At the time he was thought to be the last Union veteran, but it turned out that his Confederate counterpart – Walter Williams, who supposedly died at 117 years old – was probably a fake, so Woolson was actually the last man standing.

One of the most famous speeches in American history, the Gettysburg Address consisted of just 272 words and took only a couple of minutes for Lincoln to deliver. But the crowds that gathered on that day in November 1863, for the dedication of a cemetery on the site of the Battle of Gettysburg four months earlier, had not primarily come to hear the president.

Edward Everett, probably the best-known orator of the age, spoke for two hours without notes in a masterclass that earned high praise in the newspapers. He immediately saw the power of Lincoln’s words, however, remarking: "I wish that I could flatter myself that I had come as near to the central idea of the occasion in two hours as you did in two minutes."

Women embraced a number of roles during the war. At home, they raised funds or gathered supplies for the army while managing households and businesses. Many assisted the war effort by working as nurses – like Clara Barton, founder of the American Red Cross – or spies.

Others, however, decided to pick up a gun. Estimates suggest that between 400 and 750 women disguised themselves as men and enlisted to fight, although the true number could be higher. These included Sarah Emma Edmonds, under the name Franklin Thompson, and Sarah Rosetta Wakeman, who fought as Lyons Wakeman.

Abraham Lincoln did not lead armies personally, but other men who sat in the Oval Office did. The most obvious is Ulysses S Grant, who was elected for two terms (1869-77) thanks in part to his status as a war hero. Rutherford B Hayes (1877-81) showed remarkable courage during the war, and was wounded at least four times.

James Garfield (1881, pictured right) and Benjamin Harrison (1889-93, pictured left), both rose through the officer class, while Chester A Arthur (1881-85) was a quartermaster in New York. Finally, William McKinley (1897-1901) enlisted at 18 and fought at Antietam, rising to the rank of brevet-major.

On 9 April 1865, Ulysses S Grant, commander of the Union armies, accepted the surrender of Robert E Lee in Appomattox Court House, Virginia. In truth, some fighting continued and the proclamation formally ending hostilities would not be made until 20 August 1866, but Appomattox has gone down in history as the moment the Civil War ended.

Lincoln, whose entire presidency had been consumed by the conflict, could enjoy his victory for just five days. On 14 April, he went to see a play at Ford’s Theatre with his wife Mary, when John Wilkes Booth snuck into his box and shot him in the back of the head.

Called 'the Great Locomotive Chase', this was a daring raid by a handful of Union volunteers on 12 April 1862. Led by James J Andrews, the idea was to sneak into Georgia, steal a train and steam it back north while destroying as much track and infrastructure as possible.

It did not go to plan. Of the 24 volunteers, two were captured quickly and another two overslept. The rest managed to steal a locomotive, The General, but were quickly spotted and pursued by Confederate troops in their own train. The chase lasted seven hours, but in the end all the raiders were captured and eight were hanged.

The last person to receive a government pension from the war was Irene Triplett, the daughter of Mose Triplett. He had fought for the Confederacy before deserting while his unit was marching to Gettysburg in 1863 (where it was all but wiped out), and switching sides to the Union. When he died his gravestone simply read: "He was a Civil War soldier".

As for Irene, born in 1930, she was entitled to collect his pension of $73.13 a month from the Department of Veterans Affairs until her death, which was at the age of 90 in 2020.

Today, the Confederate flag is a divisive and controversial image, associated with white supremacy. The banner, also called the Southern Cross (a blue diagonal cross with 13 white stars on a field of red), does hark back to the Civil War, but it was never the Confederacy's official flag – that was the Stars and Bars (pictured).

The Star and Bars was not, however, a suitable battle flag, as it was too easily confused with the Union flag in the heat of battle. Instead, the Southern Cross, designed by William Porcher Miles, was used. It was flown by the Confederacy's armies but was never its official symbol.

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