Complex sentence: While in the army he edited An Cosantòir, the Irish Army's magazine, and convinced Eamon de Valera to establish the Bureau of Military History which would record personal accounts from the Irish War of Independence.
Split into simpler sentences: While in the army he edited An Cosantòir, the Irish Army's magazine. He convinced Eamon de Valera to establish the Bureau of Military History which would record personal accounts from the Irish War of Independence.