Complex sentence: Hakusensha was founded on December 1,1973 by Shueisha, but is now a separate company although still a part of the Hitotsubashi Group together with Shueisha and Shogakukan as one of the major members of the keiretsu.
Split into simpler sentences: Hakusensha was founded on December 1,1973 by Shueisha. It is now a separate company although still a part of the Hitotsubashi Group with Shueisha and Shogakukan as one of the major members of the keiretsu.