Complex sentence: Since the 1999 sale of its broadcast client list to its one-time major rival, the AP, UPI has concentrated on smaller information market niches and no longer services media organizations in a major way.
Split into simpler sentences: Since the 1999 sale of its broadcast client list to its one-time major rival, the AP, UPI has concentrated on smaller information market niches. It no longer services media organizations in a major way.