Complex sentence: Doyle remained a prominent IRA militant and took part in various acts in the early 1940's, he lived to a ripe old age and continued to take pride in having killed O'Higgins.
Split into simpler sentences: Doyle remained a prominent IRA militant and took part in various acts in the early 1940's. He lived to a ripe old age and continued to take pride in having killed O'Higgins.