How did the Exxon Valdez happen?

The Exxon Valdez happened over a series of disasters the radar didn't work the ship was on auto pilot and the captain hired some one who didn't know how to drive the ship and put them in charge and it spil.

The above answer has problems. The radar was fine. Radar is used to see weather and oncoming traffic. Sonar is used to measure depth. This was required to navigate shallow waters and did not function.

Another issue was the single hull system that was used to build the ship. Basically it is a very large single tank. The slightest hit to the hull and all of the oil would spill. A safer practice would be to have the ship with a protective inner tank so it would require a harder hit to cause a spill. Multiple tanks also reduce oil flow if the system is compromised.

The Captain, despite many rumors, was not found to be drunk at the time of the accident. He was not even on the bridge. The third mate and helmsman were in charge of the ship at the time of the hit. The individuals that were in charge of the bridge during the hit were legal and competent to have been in charge, The Captain is not in charge of hiring the crew.