@phil_stevens The US tying their dollar to everyone's oil trading means they can print infinite money without shifting their exchange rates, leaving them arbitrarily wealthy without having to produce anything of value.
Meanwhile, everyone else in the world has to be at least somewhat useful to someone.
So Iran trading oil in yuan is a huge no-no for the US. Long term, they can't survive without the petrodollar, so letting this continue is just something they can't do.
You can see this in the lead up to a lot of recent wars, and coups, national leaders announce trading oil in something other than US dollars, and then they're gone.