Which action prompted the start of the persian gulf war

Saddam Hussein's invasion of Kuwait.

Saddam Hussein's invasion of Kuwait is the right answer.

Explanation:

Persian Gulf War that took place in 1990–91 was a global struggle that was triggered by intrusion of Kuwait by Iraq on 2nd August 1990. This invasion took place when the leader of Iraq,  Saddam Hussein, planned the attack and capture of Kuwait with the obvious aim of obtaining that nation’s massive oil supplies, removing a huge mortgage Iraq owed Kuwait and developing Iraqi influence in the country.