Martial law was declared by the ROC on the morning of May 20, 1949, following an air battle over the Taiwan Straits the night before.
戒嚴，是國家遭遇戰爭或非常事變時，行政首長為維持社會治安，於全國或特定區域施行兵力戒備，並將該區行政、司法權移轉軍事機關行使，而對人民之自由權加以限制之謂。