Complex sentence: In line with all the Sinn Féin MPs elected at that election he did not represent his constituents at Westminster but withdrew to sit in the declared independent Dáil Éireann (the First Dáil) and was named by Éamon de Valera as special envoy to the United States.
Split into simpler sentences: In line with all the Sinn Féin MPs elected at that election he did not represent his constituents at Westminster but withdrew to sit in the declared independent Dáil Éireann (the First Dáil). He was named by Éamon de Valera as special envoy to the United States.