It was covered by thick woodlands 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%.
By 16,000 BC, rising sea levels due to ice melting caused Ireland to become separated from Great Britain.
These Mesolithic communities lived as hunter-gatherers across the island until about 4000 BC.
In 2011, the population of Ireland was about 6.6 million, ranking it the second-most populous island in Europe after Great Britain.
Just under 4.8 million live in the Republic of Ireland and just over 1.8 million live in Northern Ireland.
Alongside mainstream Western culture, a strong indigenous culture exists, as expressed through Gaelic games, Irish music and the Irish language.
The island's culture shares many features with that of Great Britain, including the English language, and sports such as association football, rugby, horse racing, and golf.With the Acts of Union 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.The theory holds that there were four separate Celtic invasions of Ireland.The Priteni were said to be the first, followed by the Belgae from northern Gaul and Britain.How and when the island became Celtic has been debated for close to a century, with the migrations of the Celts being one of the more enduring themes of archaeological and linguistic studies.