When was Ireland divided into north and south, and the north belonged to Britain?

/kloc-Ireland was ruled by Britain in the 0/2nd century. 1800 was incorporated into the United Kingdom of Great Britain and Ireland by treaty (China is called Britain). During this period, a large number of English people immigrated to Ireland, mainly living in Northern Ireland, and few people settled. It was the new immigrants from England who developed this area and made it prosperous. Of course, some Irish people also settled here. Later, Ireland made an indomitable independence movement and finally became a free state in 192 1. However, because the English people in six counties of Northern Ireland (accounting for 90% of the population of Northern Ireland, mainly Protestants, Irish Catholics and conflicting beliefs) are unwilling to merge into Ireland, they are willing to stay in the UK. In order to protect the interests of Protestants in six counties in Northern Ireland, six counties in Northern Ireland still belonged to Britain and 26 counties in the south established a free state through British-Irish negotiations. 1948, Ireland was completely independent and became a republic, but the six northern counties were still part of Britain, and then Britain became the United Kingdom of Great Britain and Northern Ireland.

This is the reason and process of Ireland being divided into north and south.