Complex sentence: For whatever reason, in the 73 constituencies in which Sinn Féin candidates were elected 25 were returned unopposed (17 were in Munster), although the constituencies which Sinn Féin won uncontested seats were those which subsequently showed high levels of support for republican candidates.
Split into simpler sentences: For whatever reason, in the 73 constituencies in which Sinn Féin candidates were elected 25 were returned unopposed (17 were in Munster). The constituencies in which Sinn Féin won uncontested seats were those which subsequently showed high levels of support for republican candidates.