D agreed to purchase weaner pigs, i.e., weaned piglets, from P. D intended to sell these pigs to third-party finishers, who would raise the pigs to market weight. Farmland Industries, Inc. (Farmland) then would buy market hogs from third-party finishers under the terms of an existing contract between Farmland and P. D was to buy P's weaner pigs only while Farmland purchased market hogs from third-party finishers. The Agreement depended on Farmland's purchase of market hogs from third-party finishers. Farmland subsequently refused to buy market hogs from third-party finishers, declining to consent to an assignment of the P and Farmland contract. Without the ability to sell weaner pigs to third-party finishers for sale to Farmland, D had no reason to buy pigs from P. D terminated the agreement. P sued alleging a breach. D asserted frustration of purpose as an affirmative defense. P and D both moved for summary judgment. The district court first determined D had breached the Agreement; however, it granted summary judgment to D on its affirmative defense of frustration of purpose. The district court relied on Recital D and P's testimony to determine D's principal purpose in entering into the Agreement. P appealed: the district court erred in relying on extrinsic evidence to determine D's principal purpose in entering into the Agreement.