The Thousand-World Coalition was a proposal by Capellan Chancellor Arden Baxter to form a mutual nonaggression and protection pact with neighboring Periphery worlds and states. Were it accepted, the pact would have extended to the Duchy of Andurien, the Taurian Concordat, and independent Periphery worlds which later joined the Magistracy of Canopus. 
Largely intended by Baxter to isolate the growing Free Worlds League, the pact was rejected by Taurian Regent-Protector Sigur Fonn in 2422, a result of the increasingly skittish view held by Taurians of the Inner Sphere in the wake of conflicts with both the Federated Suns and the Capellan Confederation, though the preliminary negotiations did result in a wary neutrality between the Capellan and Taurian realms. 
- The Periphery (first edition), p. 20, "Struggle with Liao"
- Era Digest: Age of War, p. 5, "War Without Reason"