Santino tried to do the same things Michael did - but unsuccessfully.

Michael wiped out Taggalia and the "rest of the Five Families." That was also Santino's intention ("There ain't gonna be no stalemate! I'm going to end it by killing that old bastard!) as he said to Tom after leaving Vito's sick bed ("I didn't mean that - Ma made dinner, its Sunday-").

Santino was strong, and he could have been a Don as successful as Michael if only he could control his emotions. Alas, that was Santino's downfall - both as a Don, and as a Person.