The American history of the term “invasion” reveals that its literal meaning is entry plus enmity: Entry alone, which is trespass, is not sufficient to constitute an invasion. Although the Framers occasionally used “invade” in a metaphorical sense, we know that in the Compact Clause they used the word in its literal sense, because that clause’s ancestor text in the Articles of Confederation refers to invasion “by enemies.” Past non-state actors, like pirates and barbarians, fell under the category of “invaders” in the opinion of certain American statesmen, such as Madison. Present-day non-state actors, like cartel-affiliated gangs operating within the territory of a U.S. state, may fall under the category of invaders, provided their criminal activity reaches a scale or degree of organization that deliberately overthrows or curtails the lawful sovereignty of the state.

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