Complex sentence: In 1926, many Anti-Treaty republicans decided to resume constitutional politics and to found the Fianna Fáil party, and in 1927 took the Oath of Allegiance and entered the Dáil (M.E. Collins Ireland 1868-1966, p.338).
Split into simpler sentences: In 1926, many Anti-Treaty republicans decided to resume constitutional politics and founded the Fianna Fáil party. In 1927 they took the Oath of Allegiance and entered the Dáil (M.E. Collins Ireland 1868-1966, p.338).