Complex sentence: The overall trend was the gradual reduction in the number of different case endings: the locative case disappeared, but the six other cases were partly retained in personal pronouns, as in "he", "him", "his".
Split into simpler sentences: The overall trend was the gradual reduction in the number of different case endings. The locative case disappeared, but the six other cases were partly retained in personal pronouns, as in "he", "him", "his".