Darrius contracted with Nathaniel on February 1st to have 5 crates of bags shipped to Nathaniel via UPS by April 1st. There was a strike soon after for the following months prohibiting any shipments via UPS. Identify the legal issue.

Darrius contracted with Nathaniel on February 1st to have 5 crates of bags shipped to Nathaniel via UPS by April 1st. There was a strike soon after for the following months prohibiting any shipments via UPS. Identify the legal issue.