Complex sentence: The North Island Main Trunk Railway came through in 1907 but not much wool was sent by rail as overgrazing by the sheep at this time had led to a plague of rabbits, and by the 1930s no sheep at all could be grazed on Waiouru sheep station.
Split into simpler sentences: The North Island Main Trunk Railway came through in 1907 but not much wool was sent by rail as overgrazing by sheep at this time led to a plague of rabbits. By the 1930s no sheep at all could be grazed on the Waiouru sheep station.