Complex sentence: Naturally it was assumed that its leader, Richard Mulcahy, would be offered the post, however, he was an unacceptable choice to Clann na Poblachta and its deeply republican leader, Seán MacBride.
Split into simpler sentences: Naturally it was assumed that its leader, Richard Mulcahy, would be offered the post. However, he was an unacceptable choice to Clann na Poblachta and its deeply republican leader, Seán MacBride.