I've asked myself what the Joker's motivation was. Since the lazy answer which allows to tell every story "He's crazy, that is the reason!" doesn't apply to Nicholsons Joker (and did not to the comic Joker before the "insanity" card was played all the time). In B89 we see that after Jack Napier is transformed he gets his revenge and kills Grissom. Then it seems that he tries to take control of the organised crime in Gotham City and to get the public attention taken away from Batman to him (IMO the reason why he poisoned the cosmetics). The rendez-vous with Vicki Vale can be interpretated as "sexual desire". And when Batman steals his "bride" from him and gets again the attention with breaking his "poison code" he decides to go for a final and direct confrontation to finish him finally. Anf if he had succeeded what would he have done? World domination?