Complex sentence: The opposition's failure to present a single candidate offered a significant advantage to Biya, as the electoral law did not provide for a second round, and therefore the opposition candidates could not unite against Biya in the event he failed to win a majority.
Split into simpler sentences: The opposition's failure to present a single candidate offered a tremendous advantage to Biya. The electoral law did not provide for a second round, and therefore the opposition candidates could not unite against Biya in the event he came up short of a majority.