South Korean President Yoon Suk Yeol on Tuesday declared martial law in an unannounced late night address broadcast live on YTN television.

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.

Parliamentary aides in South Korea emptied fire extinguishers on armed troops entering the national assembly as protesters took to the streets.

South Korea’s opposition party members gather at the country's parliament building on Dec. 4 after the president declared martial law.