Complex sentence: Four years later, another Bolivian government rejected the treaty and attempted to raise taxes on a Chilean nitrate company, so the Chilean army occupied Antofagasta, a Bolivian city.
Split into simpler sentences: Four years later, another Bolivian government rejected the treaty and attempted to raise taxes on a Chilean nitrate company. As an answer to this action, the Chilean army occupied Antofagasta, by that time a Bolivian city.