The Biden administration has hailed South Korea as a model democracy and bolstered military ties as it relies on the country as a bulwark against North Korea, China and Russia.

Though martial law isn't well defined in U.S. law, it has been imposed at the state and federal level to respond to emergencies.

South Korean President Yoon Suk Yeol's shocking late-night declaration of martial law brought years of clashes with domestic opponents, the media and even his own conservative party to a head and threw his political future into doubt.