Contractual obligations are optional obligations. A party voluntarily assumes them; otherwise, he or she does not have them. Consequently, if someone involuntarily agrees to assume an obligation, contract will not enforce that obligation. This is the idea behind the doctrine of duress.
Duress doctrine: if a party assents to a contract because of (1) an improper threat that (2) no reasonable person would resist, then (3) the contract is voidable by that party. See Restatement (Second) Contracts ยง 175(1).
Post v. Jones, 60 U.S. 150 (1856), illustrates the doctrine.