On Easter Monday, April 18, 1949, 30 years after the Easter Rising,
Éire became the Republic of Ireland, formally free of allegiance
to Britain and no longer a member of the Commonwealth.
In the following month, the British parliament confirmed the status
of Northern Ireland as part of the United Kingdom until its own
parliament choose otherwise.
It allowed the Republic of Ireland to retain the economic benefits
of Commonwealth membership and, in keeping with this, it extended
to Irish citizens resident in the United Kingdom the same rights
as British citizens.
Ireland granted British citizens residing in the republic similar
benefits, not including political rights. The republic became a
member of the UN on December 14, 1955.
It declined to join NATO, however, since this would have entailed
entering into an alliance with the United Kingdom, which retained
possession of Northern Ireland.