Complex sentence: They were also one of the founding members of the first fully professional first tier league in China, the Chinese Jia-A League, however they would struggle within the league until they won promotion back into the top tier at the end of the 2008 season.
Split into simpler sentences: They were also one of the founding members of the first fully professional first tier league in China, the Chinese Jia-A League. However, they struggled within the league until they won promotion back into the top tier at the end of the 2008 season.