Want of performance, or of an offer of performance, or any delay therein, is excused when it is prevented or delayed by an irresistible superhuman cause, or by the act of public enemies of this state, or of the United States, unless the parties have expressly agreed to the contrary.

Source: CivC 1877, § 855, subdiv 2; CL 1887, § 3479, subdiv 2; RCivC 1903, § 1173, subdiv 2; RC 1919, § 780 (2); SDC 1939, § 47.0229 (2).