Complex sentence: The clear history of "mala" sauce is still unknown, but it is widely believed that people in Sichuan province, one of the poorest provinces in Chinese history, invented strong-tasting "mala" sauce to cover up rotten meat.
Split into simpler sentences: The clear history of "mala" sauce is still unknown. Some have indicated that people in Sichuan province, one of the poorest provinces in Chinese history, invented strong-tasting "mala" sauce to cover up rotten meat.