Britain invaded Ireland.The Irish were dispossessed of their land. Cromwell tried to destroy Catholicism. Catholics had no rights and their religion was banned. The country was split in 2 & the Catholic minority in Northern Ireland were subject to state sponsered discrimination on the same level as the blacks in the Southern states of the US. This sparked the formation of the PIRA in 1969 and led to 30 years of violence between the IRA & the British/Unionsts paramiltaries. Thats it in a nutshell.