The party was founded in 1986 by Senator Adlai Stevenson III in reaction to the Democratic Party's nomination of two followers of Lyndon LaRouche in the race for high state offices. These candidates were Mark Fairchild, who was running for Lieutenant Governor, and Janice Hart, who was running for Secretary of State. Stevenson, a Democratic Gubernatorial candidate, did not want to run alongside anybody associated with LaRouche's organization.
There are a number of explanations as to how the LaRouche followers became nominees. Some believe that it simply boiled down to the names of the LaRouche candidates, which sounded less "ethnic" than those of their opponents George E. Sangmeister and Aurelia Pucinski. Hart's victory over Pucinski was likely helped by a voter reaction to Pucinski, whose father, Roman Pucinski, was a prominent opponent of Chicago Mayor Harold Washington.
Many criticized the Democrats for their failure to inform voters exactly who the candidates were, and this allowed campaigning efforts in rural areas to be very effective. "LaRouche Democrats" claimed that the Democratic Party (especially chairman Charles Manatt) was under the influence of Mikhail Gorbachev. LaRouche maintains that the population voted for his followers to take the party back from elitist bankers. In any case, most analysts (including Stevenson himself) agreed that the whole ordeal confused voters, resulting in Republican James R. Thompson winning the election. The "Solidarity Democrats" and the LaRouche supporters blame one another for the subsequent decades of Republican control in Illinois. Stevenson left politics and went on to become an investment banker.
The Solidarity Party continued to exist (completely unaffiliated with Stevenson) after the 1986 incident. This made it an easy for other small political parties to "take over" when necessary. One such group was the New Alliance Party (NAP) who was largely unknown in Illinois but still managed to run some of its candidates for local offices. NAP founder Lenora Fulani campaigned as a Solidarity Party presidential candidate in 1988 and 1992. This is interesting because Fulani works closely with Fred Newman, a former affiliate of LaRouche who broke from the National Caucus of Labor Committees to start his own political activities.