Fusion Party is a name for multiple political parties in United States history. The different parties that used the name don't share any particular political positions; instead, confederations of people from disparate political backgrounds united around a common cause individual to their situation—often opposition to a common enemy—and used the name Fusion Party to reflect the aggregate nature of their new party.
Fusion Party in Ohio and Indiana
The Fusion Party was the original name of the Republican Party in the state of Ohio. In 1854, anti-slavery parties were forming in many northern states in opposition to the Kansas Nebraska Act of 1854. While many of these state parties adopted the name "Republican", the Ohio convention adopted the name "Fusionist" or "Fusion Party", which they felt more accurately described the fusion of persons from a variety of political backgrounds, including members of the Free Soil Party, the Conscience Whig Party, and the Know-Nothing Party along with members of the Democratic Party who were opposed to slavery.
Similarly, in Indiana, the Know-Nothings were not strong enough to run candidates on their own, and so combined with Republicans and other interest groups to run candidates on the Fusion or People's Party tickets in opposition to the Anti-Nebraska movement.  
Fusion Party in South Dakota
In South Dakota, the Fusion Party was a short-lived political party that existed in the late 19th and early 20th century. The party was formed in 1896 from an alliance of Democrats, Free Silver Republicans, and Populists who were opposed to the platform of the state Republican Party. A total of 56 Fusion Party representatives were elected to the state legislature during its brief existence. In addition, Senator Richard F. Pettigrew, who served from 1889–1901, was the Fusion Party candidate for Senate in 1900, having left the Republican Party to join the Silver Republicans in 1896. South Dakota Governor Andrew E. Lee was also an elected to his second term as a Fusionist.
Fusion Party in North Carolina
North Carolina’s Fusion Party was a coalition of Black Republican and Populist Party members who cooperated in state elections and in state government between 1894 and 1900. While the involved Republicans and Populists maintained separate organizations and did not affiliate their united actions with a separate, third party, the group’s cooperation was labeled "fusion" or "fusionist" by its Democratic opponents. In the middle and late 1890s Republican-Populist cooperation resulted in new state delegations to Congress, Republican-Populist control of the state's General Assembly, Republicans and Populists in state executive offices, and a non-Democratic state supreme court. A significant number of fusionist officeholders were African American. 
- Brand, Carl Fremont. "The History of the Know Nothing Party In Indiana" (Article). Indiana Magazine of History Indiana Magazine of History, Volume 18, Issue 1. pp. 47–81. Retrieved 15 April 2016.
In Indiana as elsewhere there was a movement for a Fusion or People's party. The Know Nothings, perhaps the strongest of all the elements of the opposition but not strong enough to run a ticket of their own, determined to act with the Fusionists, to control the whole movement and to direct it in their own interests
- https://scholarworks.iu.edu/journals/index.php/imh/article/view/6056/5832 The Origin and Rise of the Republican Party in Indiana from 1854 to 1860 Title: The Origin and Rise of the Republican Party in Indiana from 1854 to 1860 Author: Charles Zimmerman Date: 1917 Source: Indiana Magazine of History, Volume 13, Issue 3, pp 211-269 Article Type: Article
- Goodspeed, Arthur (1904). The Province and the States, Vol. VI. pp. 331–358.
- South Dakota Legislature: Legislator Historical Listing.
- Kingsbury, George W. (1915). History of Dakota Territory. pp. 34–39.
- Biography of Andrew E. Lee National Governors Association.
- Powell, William S. (2006). Encyclopedia of North Carolina. University of North Carolina Press.
- Fusion Party Ohio History Central
- Fusion: Multiple Party Nomination in the United States by Steve Cobble and Sarah Siskind