Complex sentence: Learning of his father's great deeds, Garrosh returned to Azeroth with Thrall, becoming a member of the Horde and eventually warchief, after Thrall stepped down.
Split into simpler sentences: Learning of his father's great deeds, Garrosh returned to Azeroth with Thrall, becoming a member of the Horde. Garrosh eventually became warchief, after Thrall stepped down.