Pan-Celtism refers to an intellectual and political movement in the late 19th and early 20th century referring to the formation of a single Celtic state, typically based out of Ireland. The idea of Pan-Celtism began after the Irish Civil War in the 1880's as part of a potential Irish rejection of the English language and influences, and greatly influenced many of Ireland's future leaders in succeeding decades. The ideology tapered out in the 1890's and early 1900's after the massive economic boom in Ireland and the death of ideological godfather Seamus Kinney. The idea of Pan-Celtism was revived after Ireland's success in the Faroes War and its growing colonial holdings in Africa and Oceania began the idea of an Irish Empire. The idea lasted well into the 1920's during Ireland's Golden Age, during which many conservative and liberal Irish politicians regarded the conquest of Wales and the entry into a political union with Scotland as national priorities. More sobered politicians, however, were less enthused with this plan, notably heavyweights such as Eamon de Valera and Michael Collins.
During the Irish War, many in Ireland believed that an Irish victory would result in the transfer of Wales to Irish control - however, after the pro-annexation camp in France was sidelined by Sebastien Bonaparte, most French officials were unwilling to see Ireland receive any English territory either, and Ireland was gifted English colonial possessions in Africa and Asia instead. While this was seen as an added bonus to many in the Collins administration, many pro-Celtic Irish were furious.
The rise of the Christian Democrats in 1948 was viewed by many as a triump of the Pan-Celtic camp, as the Irish language saw a revival after decades of an English-speaking Ireland, and President Aidan Bair was receptive to seizing Wales while England was mired in its violent internal conflict. The Bair administration forged an alliance with the EWA to transfer Wales to Ireland once Ireland helped the EWA secure all of England proper - however, the American intervention and the ensuing undeclared war with the United States ended Irish adventurism, especially with the Bair administration's unpopularity having lost Irish East Africa, the campaign in Wales and the declining Irish economy. Pan-Celtism as a serious political movement died with the Irish withdrawal from Wales, and the proposed political union with Scotland never materialized as a result.