casus foederis

By the very terms of this guarantee, as well as by the general principles of law, the guarantors are only collaterally liable, upon the failure of the principal debtor to pay the debt. A demand upon him, and a failure on his part to perform his engagements, are indisponsable to constitute a casus foederis. The creditors are not, indeed, bound to institute any legal proceedings against the debtor, but they are required to use reasonable diligence to make demand, and to give notice of the nonpayment. The guarantors are not to be held to any length of indulgence of credit which the creditors may choose; but have a right to insist, that the risk of their responsibility shall be fixed, and terminated within a reasonable time after the debt has become due.

Lat. The case of the treaty or compact; the case or event contemplated by a treaty; a case within it, or to which it applies. 1 Kent's Com. 49. Applied to an exigency contemplated by the constitution of the United States, (the foedus of the union.) Id. 264. Applied also to an ordinary contract, as to a respondentia bond. Story, J., 4 Mason's R. 253.