A militant Republican army which split from the Official IRA in 1969 because of their refusal of violence. Started off mostly as a defence group but soon began attacks on British military personell. Primarily a green Republican group but from the mid 70s adopted a Marxist-Leninist outlook. Members have been trained in Libya and by the PLO and have maintained links with them and various other groups, including ETA and FARC.
Groups that continue to use the name and have not given into British imperialism are the CIRA, RIRA and INLA.
The Irish Republican Army originated in the 1800s and even before that, though not widely organized.