Since at least the 1600s, all of these areas have been connected politically, reaching a height in 1801 with the creation of the United Kingdom of Great Britain and Ireland. About five-sixths of the island of Ireland seceded from the United Kingdom in 1921 as the Irish Free State. Historically, relations between the two states have been influenced heavily by issues arising from their shared (and frequently troubled) history, the independence of the Irish Free State and the governance of Northern Ireland. These include the partition of Ireland and the terms of Ireland's secession, its constitutional relationship with and obligations to the UK after independence, and the outbreak of political violence in Northern Ireland. Additionally, the high level of trade between the two states, their proximate geographic location, their common status as islands in the European Union until Britain's departure, common language and close cultural and personal links mean political developments in both states often closely follow each other.