Donald Trump is under fire again, this time for his typically Trumpian history of the American Civil War.

Somehow, President Trump managed to casually glide over more than 150 years of rigorous academic history and debate to claim that the jury's still out on what caused the Civil War, which lasted for four years between 1861 and 1865 and killed at least 620,000 Americans.

Trump also praised President Andrew Jackson, who he euphemistically called a "swashbuckler".

Jackson, a racist slave-owning populist, was president between 1829 and 1837, and died in 1845 aged 78, 16 years before the Civil War had even started.

"I mean, had Andrew Jackson been a little later, you wouldn't have had the Civil War," the current president told radio host Salena Zito on her Sirius XM show.

"He was a very tough person, but he had a big heart, and he was really angry that he saw what was happening with regard to the Civil War. He said: 'There's no reason for this.' People don't realise, you know, the Civil War, you think about it, why?

"People don't ask that question. But why was there the Civil War? Why could that one not have been worked out?"

Which is an interesting interpretation of Jackson, the Civil War, and its causes. Most historians agree that, while there are many complexities and nuances, the central cause of the war was slavery.

Africans were snatched away from their homelands by slavers and sold as property to wealthy American landowners who kept them in appalling conditions, inflicted cruel tortures on them such as whipping, and forced them to work for nothing, often on plantations. Subsequent generations of African Americans were then born into slavery.

Some states wanted to maintain slavery, the source of their wealth, and formed the Confederacy to defend it as an institution. The Unionists under President Abraham Lincoln wanted the abolition of slavery across the whole of the US. "If slavery is not wrong, nothing is wrong," Lincoln famously wrote.

Several Confederate states tried to secede from the US after the anti-slavery Lincoln was sworn in as president in February 1861, fearing he would extend abolition to the whole country.

War quickly broke out as Lincoln sought to maintain the union and bring Confederate states to heel over the slavery issue, a war the Unionists would eventually win.

Jim Grossman, a historian from the American Historical Association, told the BBC:

[Trump] starts from the wrong premise - the premise that the Civil War should somehow have been avoided, and that someone more skilled on the White House could have avoided it.

If one sees the Civil War as a war of liberation, which is what it was, then it shouldn't have been avoided. Had you compromised out the differences between the government and the Confederacy, or between anti-slavery forces and southern slaveholders, the victims would have been the enslaved people of the south.

If the president has the notion that it would desirable to compromise that out, without emancipation, it is frightening.

As for Jackson, who Trump has referenced positively before, Gina Yannitell Reinhardt a lecturer in the Department of Government at the University of Essex, wrote on The Conversation in 2016:

Trump's defence [of Jackson] is understandable, because his is a special kind of racism. He doesn't exactly hate African-Americans, Latinos, or other non-whites; like Jackson, he simply doesn't respect their rights. Minorities can live their lives as long as they don't threaten the security of the white majority.

There may be no president in history that represents this notion better than Jackson, who signed the Indian Removal Act and announced with 'pleasure' the 'benevolent policy of the government' to resettle 'Indians' far from white settlements.

These tribes were not threats in themselves, but were seen as a threat to white prosperity and security. Jackson thus ordered a forced removal of tribes to regions west of the Mississippi River, during which an estimated 4,000 Cherokee and 3,500 Creeks died. These events are collectively known as the Trail of Tears.

According to the website of The Hermitage, Jackson's mansion in Nashville, Tennessee, where he is buried:

In all reality, slavery was the source of Andrew Jackson's wealth.

The Hermitage was a 1,000 acre, self-sustaining plantation that relied completely on the labour of enslaved African American men, women, and children. They performed the hard labor that produced The Hermitage's cash crop, cotton.

The more land Andrew Jackson accrued, the more slaves he procured to work it. Thus, the Jackson family's survival was made possible by the profit garnered from the crops worked by the enslaved on a daily basis.

When Andrew Jackson bought The Hermitage in 1804, he owned nine enslaved African Americans. Just 25 years later that number had swelled to over 100 through purchase and reproduction. At the time of his death in 1845, Jackson owned approximately 150 people who lived and worked on the property.