Oil was discovered in Persian in 1908 and it's been largely downhill since.
More recently - US ends Iranian nuclear agreement and increases economic pressure on Iran, Iran increases guerilla activity throughout the ME, most recently through protests/riots at the US Embassy in Iraq, US blows up a high ranking Iranian official in an Iraq airport (think Secretary of State level official), ???
Personally I think it was a poor idea for a couple of reasons - at the minimum we'll see increased troop deployment and fighting in the middle east broadly in proxy fights (I believe the US deployed 3500 extra troops this morning), and perhaps more importantly I think it sets an extremely poor precedent with the assassination of government officials (say China decides to execute some key leaders in Taiwan?), also the (hopefully somewhat low) chance for a hot war with Iran