Complex sentence: He would use his influence to depress the stock of a company, after which he would buy a controlling interest, which would increase his wealth after its value rebounded and owned among other holdings a newspaper, farmland in Tuscany, and other properties worth millions.
Split into simpler sentences: He would use his influence to depress the stock of a company, after which he would buy a controlling interest, which would increase his wealth after its value rebounded. He owned among other holdings a newspaper, farmland in Tuscany, and other properties worth millions.