The USA has been the largest bully of them all in contemporary times although in a much subtle way compared to China.
I'm an American, and I wouldn't dispute the above statement--and the US has been a global bully for many years unfortunately. It's sad that our government takes all the actions it does, from military intimidation to trade sanctions, but there's very little the average citizen can do to stop them from doing all of that--just like trying to eliminate the death penalty. Change takes place at a snail's pace.
As far as Iran's plight goes, things may change if Biden wins the election (which looks pretty likely at the moment). I get the sense that he'll try to undo a lot of what Trump did during his shameful four years as president, so hopefully the US's relations with countries like Iran, China, and others will improve. I have my fingers crossed that this is the case.
When China invades Taiwan, if the US looks the other way then relations will improve. You think Trump did the trade war for no reason? WW3 has started. India, Taiwan, Japan, S. Korea, Philippines and Australia know who the enemy is in their territorial waters. If Biden looks the other way as did Clinton, Bush, Obama then China will play nice with the US while holding stacks of USD reserve. Considering Joe was the one who announced the $535 million Solyndra free money grab I doubt he has the acuity to counter China.