How did the IRA affect Ireland?

Answer 1

The IRA was a terrorist organisation. Most of its activities were within Northern Ireland, but it did have some activities outside of it. It was one of the elements that kept the conflict going. It killed many people, including civilians, members of the British armed forces, police and members of rival terrorist organisations. It did foster some negative opinions towards Irish people, particularly in Britain, but the vast majority of Irish people did not support them in any way. It had an economic impact, through making tourists more wary of travelling to Ireland, though many of those potential tourists has the misconception that there was activity throughout Ireland and nowhere was safe, which was far from the reality. Investors and foreign companies would have been more reluctant to come too.

Answer 2

The actual Irish Republican Army under Michael Collins waged a campaign against the British which ultimately led to the establishment of the Irish Free State. The IRA later waged a war against the Free State Army. Although they lost the Irish Civil War, their actions ultimately led to the establishment of Ireland as a Republic, wholly independent of the United Kingdom.

The sectarian terrorists who nowadays fly the IRA banner haven't really had much of an impact on Irish history, although their impact on modern British history can't be ignored.