A treaty of guaranty

is an engagement by which one state promises to aid another when it is disturbed, or threatened to be disturbed, in the peaceable enjoyments of its rights by a third power. Treaties of alliance may be offensive or defensive; in the former the ally engages generally to co-operate in hostilities against a specified power, or against any power with which the other may be at war; in the latter, the engagements of the ally extend only to a war of aggre ion commenced against the other contracting party. The execution of a treaty is occasionally secured by hostages; as at the peace of Aix-la-Chapelle, in 1748, when several peers were sent to Paris as hostages for the restoration of Cape Breton by Great Britain to France. For celebrated treaties, see appropriate headings in this work.