It may be said that to some extent the 'fault lines' of Uruguay's politics have run within the historically dominant Colorado and National parties.
Uruguay underwent an intermittent series of civil wars through much of the 19th century, which ended in 1904, and the party system has in the past reflected regional loyalties which emerged during that period.
Critics of these two parties may argue that they have to some extent been compromised with the past willingness of some of their prominent members to work with the civilian-military administrations of 1973-1985.
Supporters may argue that in the difficult circumstances of the years in question such participation as was afforded by Colorado and National members to the civilian-military administrations was against the background of political figures (from both EP-FA-NM and National parties, such as Liber Seregni and Wilson Ferreira Aldunate) who were exiled and/or incarcerated, thus playing no part at all in the country's affairs until circumstances were more fortuitous for them.
Economic problems also may have substantially contributed to the Uruguayan electorate's willingness in 2004 to move away from the traditional parties.