When we talk about gray zone coercion, or gray zone aggression, we are talking about coercion that is more intense than run-of-the-mill diplomacy but less explicit and overt than a full-on military conflict. Gray zone aggressors tend to be revisionist powers; they are actors with some grievance about the current international system. But they don't wish to pay the costs of overt aggression and full-on war, whether those costs are economic sanctions, confrontation with the U.S. alliance system, or others. And so they pursue coercion in a low-key, calibrated way. A good example is Chinese island building and expansionism in the South China Sea. China is using its power in an assertive fashion to bend the regional order to its liking, by using tools ranging from fishing boats to its maritime militia to economic coercion of its neighbors. But it is remaining well below the threshold of open war.