The one reason trump started the iran war:
His ratings obsession.
He knew starting a war had worked in the past.
Bush jr's approval shot up to 92% when he started bombing afghanistan in 2001 and later to 76% when he invaded iraq.
Trump will never give a second thought to the cost of lives, let alone the monetary cost to the people of the US or the rest of the world.
Needless to say, he failed again. Gaining a 1% rise in the first 2 days, his downward spiral has once again started.