Complex sentence: These industrial firms, which employed more than 1,000 workers (including many Italians), flourished thanks to the production of explosive materials during World War I. After the war, the industry declined due to the changes of production methods and high railway tariffs.
Split into simpler sentences: These industrial firms, which employed more than 1,000 workers (including many Italians), flourished thanks to the production of explosive materials during the first World War. At the war's end, the industry declined due to the changes of production methods and high railway tariffs.