By William C. Kashatus

The Democratic Party has gone to great lengths to ensure consensus at its national convention this summer in Philadelphia. The event, scheduled for the week of July 25, will take place more than a month earlier than recent conventions, which typically fell around Labor Day.

Although the Democrats gave up the greater voter attention that comes later on in the calendar, the move was made in order to counter any bounce in the polls for the likely Republican nominee, Donald Trump, who will be picked at the GOP convention held in Cleveland from July 18 to 21.

In addition, Philadelphia was selected over New York City and Columbus, Ohio, because Pennsylvania has deep ties to Hillary Clinton, the party's presumed nominee. Clinton's father grew up in Scranton, and she spent summers vacationing at Lake Winola. Pennsylvania also gave Clinton a big win in the 2008 Democratic primary when Barack Obama was beginning to run away with the race. Many of the state's top political leaders, including former Gov. Ed Rendell, are longtime allies of Clinton, and Philadelphia has been a reliable source of campaign contributions.

But if history repeats itself, this year's Democratic National Convention will not go as smoothly as anticipated. Twice before, the Democrats held their convention in the City of Brotherly Love, and on both occasions controversy erupted.

Philadelphia's first DNC, in 1936, alienated Southern delegates by changing the nominating procedure. Prior to that time, the nomination of candidates for president and vice president required a two-thirds vote of the delegates. That rule had long given the South a de facto veto on presidential nominees.

But Franklin D. Roosevelt, who was re-nominated by acclamation without a roll-call vote, pushed to abolish the two-thirds rule in favor of a majority nomination, claiming that it would result in less balloting and allow candidates to be more easily nominated.

FDR had an ulterior motive. The rule change not only eliminated the South's veto, but it also diminished that region's clout at the convention by making it easier for Democrats to adopt civil rights and other liberal ideas into their platform.

Southern Democrats continued to decline in power, ultimately leading to the "Dixiecrat" movement and Richard Nixon's 1968 "Southern strategy" to gain support for the Republican Party by appealing to the racism of Southern voters.

Similarly, the 1948 DNC, also held in Philadelphia, was marred by a dispute over civil rights. Northern liberal Democrats led by Mayor Hubert Humphrey of Minneapolis and Illinois Sen. Paul Douglas pushed for the convention to adopt a strong civil rights platform plank and endorse incumbent Harry S. Truman's pro-civil-rights actions.

Opposed by moderates who feared alienating Southern voters - regarded as essential to a Democratic victory - Humphrey and Douglas secured the support of Northeastern urban Democratic leaders, who believed the plank would appeal to the growing black vote in their traditionally Republican cities.

When the convention adopted the civil rights plank in a close, 652-to-582 vote, all 22 members of the Mississippi delegation and 14 members of the Alabama delegation walked out.

The delegates who bolted later joined other Southerners to form the States' Rights Democratic Party ("Dixiecrats") and nominated South Carolina Gov. Strom Thurmond for president. In the absence of the three dozen Southern delegates who walked out of the convention with Thurmond, 947 Democrats voted to nominate Truman as their candidate against 263 for Sen. Richard Russell Jr. of Georgia.

The fight over the civil rights plank was a launching point for Humphrey, who was elected to the U.S. Senate that year and, in 1964, was elected vice president.

Clinton won't have to worry about the Southern delegations at this year's DNC. In the primaries, she swept the South with victories that were all in the double digits. She is extremely popular among blacks, Hispanics, and women in those states, and still retains powerful political allies in Arkansas, where she made her home for many years.

Whether controversy prevails this year or not, the Democrats can take comfort in the fact that the 1936 and 1948 conventions nominated candidates that went on to capture the presidency in the general election. No doubt Clinton and her party are hoping that historical pattern will repeat itself.

William C. Kashatus is a historian and writer.