Ireland is officially called Ireland, but sometimes referred to as the Republic of Ireland. From 1801 to 1922, Ireland was part of the United Kingdom. In 1921, the Irish War of Independence ended, and the nation gained independence. The region of Northern Ireland independently chose to remain part of the UK. Ireland has a population of 4.5 million, an area of 70,273 sq km, and a very high HDI of 0.916.