What fed the IRA? A hint, from here:

The Black and Tans did not act as a supplement to the RIC [Royal Ulster Constabulary]. Though some men were experienced in trench warfare, they lacked the self-discipline that would have been found in the Western Front. Many Black and Tan units all but terrorised local communities. Community policing was the preserve of the RIC. For the Black and Tans, their primary task was to make Ireland "hell for the rebels to live in". Over 8000 Black and Tans went to Ireland and while they found it difficult to cope with men who used classic guerrilla tactics against them, those who lived in areas where the Black and Tans were based, paid the price.

The attitude of the Black and Tans is best summed up by one of their divisional commanders:

"If a police barracks is burned or if the barracks already occupied is not suitable, then the best house in the locality is to be commandeered, the occupants thrown into the gutter. Let them die there – the more the merrier.
Should the order ("Hands Up") not be immediately obeyed, shoot and shoot with effect. If the persons approaching (a patrol) carry their hands in their pockets, or are in any way suspicious-looking, shoot them down. You may make mistakes occasionally and innocent persons may be shot, but that cannot be helped, and you are bound to get the right parties some time. The more you shoot, the better I will like you, and I assure you no policeman will get into trouble for shooting any man." (Lt. Col. Smyth, June 1920)

The most infamous attack on the public came in November 1920. Many people had packed into Croke Park, Dublin, to watch a football match. In retaliation for the murder of fourteen undercover detectives by the IRA, the Black and Tans opened fire on the crowd, killing twelve people. In retaliation for this attack, eighteen members of the ‘Auxies’ (a separate part of the Black and Tans) were killed in Kilmichael, County Cork. The ‘Auxies’ took their revenge for this by burning down the centre of Cork and parading around after this event with burnt cork in their caps. Violence, it appeared, only led to even more violence on both sides.

The Black and Tans were not regular troops. There were many examples of them shooting indiscriminately at civilians as opposed to republican guerrillas. Creameries were also destroyed by the Black and Tans – almost as a way of economically punishing those who may have been helping the IRA. Those experienced in trench warfare fighting a seen enemy, were of little use in Ireland. The Black and Tans were so poorly disciplined and trained for Ireland that their casualty rate was far higher than could have been imagined when the government first advertised for them. The government in Westminster quickly realised that they were a liability as even public opinion in mainland Britain was appalled by a lot of what they did.

What did the Black and Tans achieve? They served no purpose for the British government as they simply failed to stop what the IRA was doing. However, they did succeed in getting the republican cause a great deal of civilian support simply because of their acts – people may not have joined the IRA, but they were supporters of it and gave what financial help they could to the movement. The Black and Tans were pulled out of Ireland in ignominy.

The Irish themselves have stepped up to stop the violence more recently. We seem to forget that savagery toward the grandparents and great-grandparents of those living there now by the poor British, who have not had a good record of humane behavior in Ireland for these 500 years, caused more ordinary Irish people to support the IRA and its predecessors than were originally inclined to do so.

Funny that people whose nation got a kickstart from British soldiers shooting a few rockthrowers dead in the streets of Boston should not care about Croke Park. Nor, probably, Bloody Sunday, even though many of us were alive for that. Give credit to the British government: it only took from 1972 until 1998 to decide it was worth a real hearing and not something which (as expressed by Lord Widgery, the judge leading the original inquiry) should take as little time as possible.

A lot of blood has been shed in Ireland. Most of it has been Irish, and not a little of that at the hands of British soldiers. Don't forget that.