Manchester United has a strong fan base, more money, and more skill than Manchester City.
Something drastic would have to happen to topple such a massive dynasty. The fan following for Manchester United can be seen and felt all over the world, even in places where football is not followed. This shows the enormous amount of influence the club has in the world. If Manchester City wants to compete, the first thing that needs to happen is the owners will need to invest massive amounts of money in player salaries and advertising. Only then will Manchester City exceed Manchester United as the top club in Manchester.