RALEIGH, North Carolina - The United States on Tuesday marked the 150th anniversary of the start of its Civil War, a bloody conflict that historians say still deeply influences the country.

"The Civil War is one of the most significant events in American history in terms of the way the American nation was defined," said William Link, a historian at the University of Florida.

Civil War re-enactors are joined by people impersonating movie characters at the Ohio Statehouse lawn to mark the 150th anniversary of the US Civil War, on Sunday. [Photo/Agencies]

More than 500,000 people were killed in the deadliest war in US history when the North and the South battled over states rights and slavery. Fighting began April 12, 1861, with an attack on Fort Sumter in South Carolina.

The country has made significant progress - electing in 2008 its first black president - but historians and political scientists say race relations and states rights are still major issues.

"We don't have slavery any more, but I think still in this country when people think of race they think of white people and non-white people, so there's kind of two groups," Link said.

Southern states, forming the Confederacy, sought their independence from the United States - the Union - arguing that tariffs imposed by the federal government hurt the Southern economy. They launched the attack on Fort Sumter.

Slavery was still legal in the South, which some historians say was the real reason for the divide.

"The primary goal of the Confederacy was to preserve a slave system," said David Kilroy, a historian at Nova Southeastern University in Florida.

President Abraham Lincoln's Emancipation Proclamation in January of 1863 declared freedom for all slaves in the Confederacy, and began a transformation that eventually ended slavery and extended civil and political equality to African-Americans, Kilroy added.

Despite the Union's victory in 1865, Southern states decades later still used state-sanctioned laws, like poll taxes, to discriminate against black people. It wasn't until the 1964 Civil Rights Act that racial discrimination was outlawed and backed up with threat of federal enforcement.

And even today there are reminders of the old divisions, particularly with states' rights.

Just two years after Barack Obama's election, voters vented their frustration with him and fellow Democrats by putting the Republicans in charge of the House of Representatives. The main sources of their anger were perceived federal mandates like the sweeping healthcare reform initiative.

"Much of the political rhetoric today is couched in absolute terms, with little or no room left for compromise and moderation," Kilroy said.

"Particularly in the Tea Party movement, there is a strong propensity to portray opposition views as the antithesis of the founding principles of the American republic, something that was common in the Civil War."

Among regular US citizens, there is no consensus about the primary cause of the Civil War. The Pew Research Center found that 48 percent of people say the war was about states' rights while 38 percent say it was mainly about slavery.

Elected officials have found that Civil War issues can be political minefields.

In Virginia - a former Confederate state home to many Civil War battles - Republican Governor Robert McDonnell, who is white, publicly apologized in 2010 for omitting slavery when he declared "Confederate History Month".

And Mississippi Governor Haley Barbour, a white Republican who is mulling a run for president, made headlines recently when he stated his belief that slavery was the main cause of secession - not states' rights.

Despite lingering racial issues, new figures from the US Census Bureau show that black Americans are returning to the South, which now has the largest percentage of black people since 1910.

Between 1910 and 1970, huge numbers of African-Americans moved to the North or Midwest in search of jobs and to escape segregation.

Agence France-Presse