I want to know the answer to the following question:
What competition sparked the rivalry with Manchester?
All the background I'm provided with is that "In addition, Arsenal and Manchester United developed a strong on-pitch rivalry in the late 1980s, which intensified in recent years when both clubs were competing for the Premier League title – so much so that a 2003 online poll by the Football Fans Census listed Manchester United as Arsenal's biggest rivals, followed by Tottenham and Chelsea.". Is that enough to answer the question?
Answer: yes