A formal agreement among nations to unite for a common cause?
Such a written document would be a treaty between two or more sovereign states. Examples include the Treaty of Versailles that followed World War I, or the NAFTA agreement on North American trade.When they bind countries to future actions, they may be called pacts. An example would be the Anti-Comintern Pact (1937) between Germany and Japan, because both were rivals of Soviet Russia.