Partition of Ireland
The partition of Ireland () divided the island of Ireland into two distinct jurisdictions, Northern Ireland and Southern Ireland. It took place on 3 May 1921 under the Government of Ireland Act 1920. Today the former is still known as Northern Ireland and forms part of the United Kingdom, while the latter is now a sovereign state also named Ireland and sometimes called the Republic of Ireland.
Ireland–United States relations
The Irish War of Independence ultimately ended with the Anglo-Irish Treaty, which confirmed the partition of Ireland into the Irish Free State and Northern Ireland, the latter of which opted to remain a part of the United Kingdom. The Irish Free State quickly fell into the Irish Civil War between Pro-Treaty Forces who supported independence via partition and Anti-Treaty Forces who opposed partition and wanted independence for the entire island of Ireland. Pro-Treaty Forces won the Irish Civil War in 1923, and the following year the United States recognized the Irish Free State and established diplomatic relations with it. The Irish Free State was succeeded by the new state of Ireland in 1937, and formally declared itself a republic in 1949.