This was a very dangerous development since the Saudi kingdom, which contained another 20% of the world's oil reserves, was militarily weak and liable to be easily over-run by the battle-hardened Iraqis. Saddam's control of such a vast proportion of a resource on which the world's economy depended was simply unacceptable for the rest of the world ("The Gulf War"). As a result, the UN Security Council passed a series of resolutions, giving a deadline to Iraq for withdrawing its forces from Kuwait and authorizing military action by the coalition force, if it failed. In a foolish act of defiance, Saddam chose to ignore the ultimatum, and suffered a crushing defeat in the war with the coalition...

It was one of the few justifiable wars in recent history because failure to confront Saddam militarily at the time would have emboldened him into further aggression against his neighbors.
Works Cited

Rayment, W.J. "The Gulf War." in-depth Info. 1999-2007. March 15, 2007. http://www.indepthinfo.com/iraq/

Iraq accused Kuwait of drilling for oil diagonally across its borders; was irked at Kuwait's refusal for foregoing loans made to his country during the Iran-Iraq war, and claimed that Kuwait was historically part of Iraq anyway

Saddam was also suspected of possessing biological weapons and on the brink of developing nuclear weapons