Mercia, officially Kingdoms and Lands Represented in the Council of the Diarchal Crowns of the Disciples is a transcontinental unrecognised nation located mainly within Cornwall on the island of Great Britain and the Prague plain in Central Europe, with colonies in North America. To external observers, Mercia may be best described as a micronation with little aspirations for independence, mainly focusing on the cultural and political aspects of nationhood.

Mercia is a long-lived and stable democratic state, guided by the two ruling diarchs of Mercia. The politicial culture and history of Mercia can be thought of as one of the most advanced in the larger micronational community. Mercia is also an established player in the world of micronational diplomacy, with membership in various micronational organisations and diplomatic relations with many like-minded micronations.