Complex sentence: The violent outbreaks in the late 1960s encouraged and helped strengthen military groups such as the IRA, who posited themselves as the protectors of the working class Catholics who were vulnerable to police and civilian brutality.
Split into simpler sentences: The violent outbreaks in the late 60's encouraged and helped strengthen military groups such as the IRA. The IRA believed themselves to be the protectors of the working class Catholics who were vulnerable to police and civilian brutality.