Complex sentence: He fled Russia and settled down in the United States where he and his second wife, Elena Gratcheva, went on to found the Internet firms, KMGi, an advertising agency, and Publicity Guaranteed, a public relations firm.
Split into simpler sentences: He fled Russia and settled down in the United States. He and his second wife, Elena Gratcheva, established the Internet firms, KMGi, an advertising agency, and Publicity Guaranteed, a public relations firm.