The contracts, the obligation of which is secured from impairment by the States, include agreements between the States and between a State and an individual or individuals, as well as those between individuals. In other words, the State when contracting does so upon the same terms as a private individual or corporation, and may not plead its sovereignty as justifying subsequent action upon its part impairing the contractual obligations which it has assumed. Its non-amenability to suit may, however, enable a State to avoid the performance of an agreement which it has undertaken to perform. This branch of the subject is more fully discussed in the chapter of this treatise dealing with the Suability of the State.6