Complex sentence: All of the developers from Bethesda Softworks moved to Bethesda Game Studios in 2002, when Bethesda Softworks and Bethesda Game Studios became separated between publisher and developer.
Split into simpler sentences: All of the developers from Bethesda Softworks moved to Bethesda Game Studios in 2002. Then Bethesda Softworks and Bethesda Game Studios became separated between publisher and developer.