This is a specific type of MacGuffin that is being sought because it will allow you to rule. Or if you're already a ruler it will allow you more or less unchecked expansion as you Take Over the World This crosses over with other tropes - usually it's an Artifact of Doom so powerful none will dare stand against you. However it can instead be more benign, a Cool Crown or Staff of Authority which magically confers kingship. The main point is that the story considers a single item essentially a Golden Snitch that makes your rulership and/or conquest a foregone conclusion. Do We Have This One? before I flesh it out?
Hello, Unknown Troper. You'll need to get known to lend a hand here.