President Yoon Suk Yeol of South Korea declared emergency martial law on Tuesday night, then reversed himself hours later as thousands of protesters flooded the streets, capping an extraordinary night of tumult in the deeply divided country.

       The threat of military rule had brought political chaos to one of America’s closest allies in Asia and carried echoes of South Korea’s postwar years of military rule and political violence.

       But Mr. Yoon’s gambit appeared to quickly backfire, leaving his political future uncertain and the opposition baying for his impeachment.

       His announcement imposing martial law, at 10:30 p.m. local time on Tuesday, had immediately raised questions over whether the president could commandeer such a highly developed industrialized democracy.

       Before dawn on Wednesday, those questions appeared to be answered.

       The National Assembly quickly passed a resolution demanding an end to martial law, and Mr. Yoon backed down, saying he would lift his emergency declaration just five and a half hours after he had issued it.

       Martial law was formally lifted at a Cabinet meeting early Wednesday.

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       President Yoon Suk Yeol of South Korea declared emergency martial law on Tuesday evening.Credit...Ahn Young-Joon/Associated Press

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