May 3 - 1921 - The Partition of Ireland
In the Government of Ireland Act 1920, the British Parliament officially granted limited home rule for the island of Ireland, but only by being split into "Northern Ireland" and "Southern Ireland" in May of 1921. This was largely a reflection of the Protestant-Catholic divide across the island, which had been a rift in the population for centuries. When the Partition came into effect, "Southern Ireland" was well on its way to winning independence from Great Britain in a War of Independence, becoming the Irish Free State. Northern Ireland, meanwhile, mostly was happy to stay as a constituent component of Great Britain. Really, the Government of Ireland Act reflected the ideas of "Home Rule" that were prevalent before World War I, when the opposition came from Ulster Loyalists in Northern Ireland. By 1921, the area that would become the Republic of Ireland was largely wanting to set up a new nation, and the actual partition was largely a formal acknowledgement of centuries old dividing lines. Yet it also firmly established the battle lines for conflicts in Northern Ireland that would lead to the Troubles in the late 20th century.