Ireland became independent, but why did Northern Ireland stay in Britain?

Britain used ethnic and religious differences to divide Ireland into Ireland and Northern Ireland, which led to Ireland's independence. However, Northern Ireland stayed in Britain, and even Northern Ireland was divided into people who stayed in Britain and people who left Britain, which troubled Britain. ?

1542, in order to better rule the island of Ireland, England moved a large number of Scots and English people to the northern part of the island of Ireland in the next few hundred years.

Therefore, the residents on the island of Ireland are divided into two parts: first, Irish people living in south-central Ireland mainly believe in Catholicism; Second, immigrants from Great Britain, living in six counties of Ulster province in northern Ireland, mainly believe in English Protestantism.

From 65438 to 0845, a great famine broke out in Ireland, and a quarter of the population died of hunger. The great famine led to the rise of the Irish independence movement.

Due to ethnic and religious differences, six counties in Ulster opposed Irish independence, while Britain separated six counties in Ulster from Ireland and established Northern Ireland.

After the Irish War of Independence, Britain split the island of Ireland by using ethnic and religious differences, so Northern Ireland remained in Britain.

The Irish who stayed in Northern Ireland wanted to leave England. In the 1960s, armed conflict broke out between Northern Ireland students studying in Britain and those leaving Britain, and the Northern Ireland issue has troubled Britain ever since.

At this point, although Ireland became independent, some Irish people who stayed in Northern Ireland still wanted to be independent and get rid of British control, and those who left Britain with Northern Ireland were also fighting with those who stayed in Britain, and even armed conflicts broke out. And give Britain a headache because of this problem.