Complex sentence: One of the co-founders was Jóhanna Sigurðardóttir after she lost an internal election for the leadership of the Social Democratic Party and members of the former communist People's Alliance.
Split into simpler sentences: One of the co-founders was Jóhanna Sigurðardóttir after she lost an internal election for the leadership of the Social Democratic Party. She was joined by members of the former communist People's Alliance.