I don’t get what Yoon was thinking declaring martial law knowing full well the Democratic Party who holds a majority in the National Assembly can just vote to end it. We all know the DP is conducting the impeachments in effort to protect their leader Lee Jae-myung from prosecution, but their had to be better response options than martial law:

President Yoon Suk Yeol declared emergency martial law, accusing the nation’s opposition of paralyzing the government with “anti-state activities,” but the National Assembly voted to lift the decree hours later.
“Martial law is aimed at eradicating pro-North Korean forces and to protect the constitutional order of freedom,” Yoon said in an emergency national address televised live in late Tuesday.
It marks the first declaration of emergency martial law in South Korea since 1979.
The surprise announcement came after the opposition Democratic Party (DP) railroaded a downsized budget bill in the parliamentary budget committee, and submitted impeachment motions against a state auditor and the chief prosecutor.
Under the Constitution, the president can declare martial law in response to military needs during times of war, armed conflict, a national emergency, or when public safety and order require it.
Following the address, Army Chief of Staff Gen. Park An-su, who was named as leader of martial law command, announced a decree banning all political activities, including protests and activities by political parties.
At at around 1 a.m, Wednesday, the 300-member National Assembly convened a plenary session to demand that Yoon lift martial law, with the resolution approved with 190 members present and 190 votes in favor.
With the motion’s passage, the martial law declaration is void, according to the parliamentary speaker’s office. (Yonhap)
You can read more the link, but Yoon was already very unpopular and this martial law decree will likely make him even more deeply disliked in Korea.