Complex sentence: The resulting fire ignited about 90,000 kg (or about 200,000 lb) of gunpowder stored there by the Republic of Venice, causing a massive explosion which destroyed about one-sixth of the city.
Split into simpler sentences: The resulting fire ignited about 90,000 kg (or about 200,000 lb) of gunpowder stored there by the Republic of Venice, causing a massive explosion. Ths explosion destroyed about one-sixth of the city.