Irish language
Until the 19th century, most people in Ireland spoke Irish, but that changed after 1801 when Ireland joined Britain to form the UK. Ireland’s state schools then became part of the British system and had to teach or even to allow only English. The Catholic Church also began to discourage Irish. Also, the Irish Nationalist leader Daniel O'Connell was an Irish-speaker himself, but he thought that people should speak English since most job opportunities were in the English-speaking US and the wider British Empire.