Examples include the Irish Parliamentary Party which pushed for Home Rule in Ireland in the late 19th century. Challenging parties also usually appeal for votes on the basis that they will try to change the voting system to make it more competitive for all parties. Structural barriers to power Third parties face an uphill battle in terms of electoral success due to incentives placed on voters by election algorithms. Even in instances where the potential supporter may align themselves most with a certain third party, in the face of overwhelming odds against impacting the election it makes more sense to just stay home or back a coalition party in compromise. These disincentives exist primarily in the United States perpetuating two-party rule and can be alleviated through adopting electoral reform measures in the form of voting system adaptations, which, predictably, are often backed by third parties and opposed by the primary parties. In some countries like the United States, parties with low win probability also face frequent exclusion from major debates and media coverage and denial of ballot access as well as hamstrung campaign budgets. United States In the United States, there have been numerous "third parties". The largest since the mid-20th century are the Libertarian and Green Parties. United Kingdom In the United Kingdom, a third party is a national political party, other than the Conservatives and Labour, which has at least one member in the House of Commons. From 1922 to 2015, Liberal Democrats and its predecessor Liberals was the third party. Since 2015, it is used for the Scottish National Party. In Scotland, the SNP has been the dominant parliamentary party beginning with the 2011 Scottish Parliament election, with the Conservative the next largest party and Labour becoming Scotland's third party ever since. Canada In Canada nearly 50+ active political parties exist throughout the nation with several of them at both the provincial and federal levels. See also Frivolous political party Vote splitting References Political parties Types of political parties