Complex sentence: The Siege of Toma was a siege between 14--17 September 1914 after troops of the ANMEF surrounded Toma, preceding to bombard it with a 12 pound field piece, which caused the Germans to negotiate a surrender.
Split into simpler sentences: The Siege of Toma took place between 14--17 September 1914, when troops of the ANMEF surrounded Toma. They finally brought up a 12-pound field piece to to bombard it, which caused the German garrison to negotiate a surrender.