Yet. And not for lack of trying on their part.

They won't be. They can't be. The world is too big and has too many countries for that to happen. If China were to decide to stop exporting stuff, it would hurt - but that's it. You couldn't replace anything that you rely on China to produce immediately, but neither is anything China's producing truly irreplaceable given a few years. Those few years would be painful, but not fatal. It's why OPEC never got to rule the world, despite having their finger on the trigger of the Oil Weapon. Sure, they had the power to induce a recession in the U.S. (or globally) any time they wanted, but that's not enough of a sword to hold over the U.S.' heads to have any real dominance.

Plus, this sort of "power" is very much like having a hand grenade in an elevator. If we were in an elevator, and I had a hand grenade, and I told you that you had to give me your wallet....would you? Sure, I'm holding a hand grenade - which means I have the power to maim or kill you if you don't do what I say. But I'm in the elevator, too. I would also get badly hurt or killed if I pulled that pin. Since I'm holding the hand grenade, I have more control over the situation than you do. But at the end of the day that doesn't get me all that much.