Saddam Hussein went to war with Iran because of his fear from the Shiites majority in Iraq.
In 1979, the Iranian revolution succeeded. Saddam was afraid it would spread to Iraq, so he tried to destroy the new Iranian regime. He brought up the issue of the border & the water war (propaganda). But he wanted the Iranian oil fields in the near the border to tip the scale of power to his favor. However, he got trapped in a long war, which lasted for 8 years.
For a similar reason, he decided to invade Kuwait. After the war with Iran, Iraq's economy was destroyed. Soldiers returned home & were shocked at the troubles they found. Saddam was afraid that the unhappy Iraqis who got used to war would unleash their fury on him. So, he decided to send them to Kuwait. Either they succeed to steal its wealth, or he gets rid of them in another war. This is why he kept the enlisted in the front lines, while the loyal Republican Guard was kept behind to bug away.