Complex sentence: In 1998 it merged with Worldwide Television News (WTN), a subsidiary of the British news broadcaster Independent Television News (ITN) and formerly known as "UPITN" as it was a joint venture between ITN and United Press International, to form APTN.
Split into simpler sentences: In 1998 it merged with Worldwide Television News (WTN). Originally though, it was a subsidiary of the British news broadcaster Independent Television News (ITN) and formerly known as "UPITN" as it was a joint venture between ITN and United Press International, to form APTN.