[dropcap]P[/dropcap]residential addresses to the United Nations General Assembly don’t get a lot of press here at home, but they do matter to listeners around the world. And those who heard President Trump’s first such address may have noticed one concept repeated throughout: sovereignty.

Most American high school students learn about sovereignty in the domestic context: popular sovereignty, or the notion that power rests with the people, is one of our political system’s most ad...