> "We're working with G20 nations to agree to a global minimum corporate tax rate that can stop the race to the bottom."
The race to the bottom Yellen refers to is corporations playing one country off another, as in "lower your taxes or we'll move our profits to Ireland." The proposed solution - countries agreeing with each other not to lower the corporate tax rate below some limit - is an example of sovereign nations working together in a way that benefits both sides, not one sovereign nation dictating policy to another.
More generally, this is a variant of a mutual coordination problem in game theory, in which it is everyone's interest for everyone to cooperate, but in each individual's interest to be the only party that doesn't cooperate. Those are notoriously tricky to induce/enforce agreement on, but it has been done.
How fair.
The news here is that US policy seems to be moving to align with smaller powers, not the reverse.
I presume it would be via some convention which allows tit for tat reciprocity and so on.
edit: think of it like this - you have the "right" to eat meat. But if I refuse to be friends with people who eat meat and you need my friendship, you can't eat meat.
Or, more realistically, the developed countries will pull any of the dozens of levers to make non-cooperative countries' life miserable.