First Gulf War question?

When George H. W. Bush announced that The U.S. would be going to war with Saddam he noted how Saddam had "crushed" Kuwait and that its people had been "brutalized." But before the war we were on pretty good terms with Saddam and did nothing while Saddam had thousands of Iraqis chemically ged and killed. What was the argument for going into Kuwait to protect the people from Saddam while we had been allowing Saddam to brutalize his own people?