With conflicts underway inside the convention hall between factions of GOP delegates and demonstrations on the streets outside, the 2016 Republican convention in Cleveland could turn out to be one of most contentious ever.
Much will depend on the words of Republicans nominee Donald Trump, experts say, as well as the actions of police in keeping the peace between his supporters and protesters. Whatever happens this week in Cleveland, it's worth looking back at some of the most controversial conventions – both Republican and Democrat – in our nation's history.
1860 Democratic
Democratic nominee Stephen A. Douglas was the Northern candidate. Credit: Library of Congress
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With the Civil War on the horizon, the Democrats split among North-South lines, and even had two separate conventions. The first in Charleston, S.C., was deadlocked after attempts to nominate Stephen A. Douglas failed. A second convention in Baltimore two months later finally pulled some of the party together, but southern delegates split and picked their own man, vice president and Kentuckian John Breckenridge (who later joined the Confederate Army and was convicted of treason). The resulting divide of the Democratic Party led to the election of Republican Abraham Lincoln, who won only 40 percent of the popular vote.
"They nominated two separate candidates, and split what could have been a majority vote," said Allan Lichtman, history professor at American University in Washington. "That changed the whole course of history."
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1924 Democratic
John W. Davis won after 103 ballots.
Credit: Library of Congress
Perhaps the most unusual convention was 1924 Democratic event in New York's Madison Square Garden that took 103 ballots and went on for 16 days. The party had to chose its nominee with two-thirds of delegates, rather than today's majority. Al Smith and Williams Gibb McAdoo (who drew support from members the Ku Klux Klan) kept splitting the vote, until a relative unknown John W. Davis finally got the nomination. Davis was unheard of in 1924, was crushed in the general election by Calvin Coolidge, winning only 28 percent of the popular vote.
WATCH: What Is the Ku Klux Klan?
1952 Republican
Convention floor fights led to a power blackout.
Credit: Library of Congress
The battle between supporters of Gen. Dwight D. Eisenhower and Sen. Robert A. Taft led to fistfights between delegates on the convention floor.
It got so bad that the convention manager pulled the plug on the power at the Cook County Amphitheater in Chicago and plunged it into darkness, said David Stebenne, professor of history at Ohio State University. "Watching on TV at home, the screen went dark and you're not sure who the nominee is," Stebenne said.
1964 Republican
Klan members supported Goldwater during this "Republican Woodstock."
Credit: Library of Congress
This "Republican Woodstock" at the Cow Palace in San Francisco was remembered mostly for nominee Barry Goldwater's hard-line conservative acceptance speech in which he declared "extremism in the pursuit of liberty is no vice."
But it was also a convention in which moderate Republicans like Nelson Rockefeller were mocked or silenced, according to Lichtman, where southern delegations were segregated by race, and when NBC newsman John Chancellor was arrested while reporting from the convention floor. This came after former president Dwight Eisenhower's speech blasting the press as too liberal.
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1968 Democratic
An officer struggles with an antiwar demonstrator outside Democratic headquarters as demonstrators attempt to break through police lines to move the protest to the 1968 Democratic National Convention. Credit: APA/Getty Images
Riots in the streets of Chicago, and television images of police beating protesters with billy clubs led to charges of "Gestapo tactics" by mayor Richard Daley.
Inside the convention, Democrats were struggling without front-runner Robert F. Kennedy, killed by an assassin's bullet in June 1968. Democrats nominated Hubert Humphrey, a party insider who had not run during the primaries. That divisive selection later forced Democrats, and later Republicans to endorse the state-by-state primary system that we have today.
2016 Republican
Republican U.S. presidential candidate Donald Trump appears onstage to introduce his wife Melania at the Republican National Convention in Cleveland on July 18, 2016. Credit: Reuters
In the generation since 1976, there hasn't been a contested convention. There also hasn't been a party outsider like Donald Trump, Stebben said. "The Republicans have historically been more organized and were a more TV- and radio-savvy party. Most are more scripted. This one is unusual."
Recent violence by and against police, and anti-immigrant comments by Trump have raised fears of potential violence in Cleveland this week.
"There may be problems outside the convention hall," said Kyle Kondik, managing editor of Sabato's Crystal Ball, a political website. "But it seems that the resistance to trump has crumbled. Maybe there will be a symbolic walk out. To me it will not be like recent divisive conventions."
Stebben says that Trump's acceptance speech on Thursday, and the police response to protests will determine how Cleveland's convention is remembered.
WATCH: History of Protests at National Conventions