Complex sentence: Their popularity initially declined from levels achieved by the Socialist Electoral League, however their seat count rose to its peak after the 2001 parliamentary election, this election marked the Socialist Left's largest voters count, earning 12.5% of the national vote.
Split into simpler sentences: Their popularity initially declined from levels achieved by the Socialist Electoral League. Their seat count rose to its peak after the 2001 parliamentary election; this election also marked the Socialist Left's largest voter count, with 12.5% of the national vote.