Ireland is an island in the North Atlantic to the west of Great Britain, from which it is separated by the North Channel, the Irish Sea and St Georges Channel, and after which it is the largest island of the British Isles archipelago. It is the third-largest island in Europe and the twentieth-largest island on Earth.Politically, Ireland is divided between the Republic of Ireland, which covers five-sixths of the island, and Northern Ireland, a part of the United Kingdom, which covers the remaining area and is located in the north-east of the island. The population of Ireland is about 6.4 million. Just under 4.6 million live in the Republic of Ireland and just over 1.8 million live in Northern Ireland.The island's geography comprises relatively low-lying mountains surrounding a central plain, with several navigable rivers extending inland. The island has lush vegetation, a product of its mild but changeable oceanic climate, which avoids extremes in temperature. Thick woodlands covered the island until the Middle Ages. As of 2013, the amount of land that is wooded in Ireland is about 11% of the total, compared with a European average of 35%. There are twenty-six extant mammal species native to Ireland.Prehistoric Ireland saw the arrival of humans after 8000 BC. Gaelic Ireland had emerged by the 1st century and lasted until the early 17th century. The island was converted to Christianity from the 5th century onward. Following the Norman invasion in the 12th century, England claimed sovereignty over Ireland. However, English rule did not extend over the whole island until the 16th–17th century Tudor conquest. This led to colonization of Ireland by settlers from Britain. In the 1690s, a system of Protestant English rule was designed to materially disadvantage the Catholic majority and Protestant dissenters, and was extended during the 18th century. In 1801, Ireland became a part of the United Kingdom. A war of independence in the early 20th century was followed by the partition of the island, creating the Irish Free State, which became increasingly sovereign over the following decades, and Northern Ireland which remained a part of the United Kingdom. Northern Ireland saw much civil unrest from the late 1960s until the 1990s. This subsided following a political agreement in 1998. In 1973, both parts of Ireland joined the European Economic Community.Irish culture has had a significant influence on other cultures, especially in the fields of literature and, to a lesser degree, science and education. Alongside mainstream Western culture, a strong indigenous culture exists, as expressed for example through Gaelic games, Irish music, and the Irish language. The culture of the island has also many features shared with Great Britain, including the English language, and sports such as association football, rugby, horse racing and golf.