Well, he did. If you recall carefully, he had wmd that he failed to register with the un inspection team. (He had made them before, they were cataloged by the un and he was supposed to submit to periodic inspection to make sure they were still under seal). After the us invaded, those and were found, of course still under seal and not a threat to anyone. The us quietly took them away to be disposed.
Basically, either Hussein was incompetent or he was trying to play a game of brinkmanship with the international community that he lost. Whether or not his actions justified invasion by the us is debatable (I do not believe so). Also the us repeatedly blatantly misrepresented Hussein to paint him as collaborating with "terrorists". but the fact is he did have wmd.