On July 15, 1987, under successive waves of the island's democratic movement and pressure from the international community, then-President of the Republic of China, Chiang Ching-kuo, announced the lifting of martial law. This ended Taiwan's 38-year period of martial law.
The "Declaration of Martial Law in Taiwan Province" was originally promulgated May 19, 1949, and took effect the next day. It was a product of the civil war between the Kuomintang (National People's Party, KMT) and the Chinese Communist Party (CCP). At that time, in the name of preventing CCP infiltration, the KMT government, which had retreated to Taiwan, implemented military control and a state of emergency. This martial law restricted the Taiwanese people's freedoms of speech, press, and assembly. The government implemented ideological social education based on Sun Yat-sen's Three Principles of the People (briefly, civic nationalism, people's governance, and popular welfare), while also using coercive means to monitor anyone and anything that could endanger the regime. This marked the beginning of Taiwan's long White Terror period.
In the 1970s and 1980s, the KMT government was facing growing diplomatic and a domestic crises. On the diplomatic front, the United States broke off diplomatic relations with the Republic of China in 1979 and established diplomatic ties with the People's Republic of China (ruled by the CCP) instead. Taiwan fell into a state of isolation, and desperately sought new ways out. At the same time, the wave demanding democratic reforms in Taiwan was surging. First the Zhongli Incident, then the Formosa Incident, became turning points on the road to lifting martial law.
After martial law was lifted in 1987, the bans on political parties and newspapers were lifted as well, and political movements sprang up like mushrooms after the rain. However, at that time, the central government could still suppress dissidents holding political views opposed to those of the central government, in accordance with the Statute for the Punishment of Treason and with Article 100 of the Criminal Code of the Republic of China. This White Terror period didn't truly end until 1992. According to later official estimates, c. 140,000 people were innocent victims during the martial law period, and more than 200,000 political victims were subjected to military trials.
References: [BBC中文網("BBC News Chinese Edition")(Chinese)(1)] (https://www.bbc.com/zhongwen/trad/chinese-news-40593296); [(2)] (https://www.bbc.com/zhongwen/trad/world-46719017); [中央社("Central News Agency")(Chinese)(1)] (https://www.cna.com.tw/news/firstnews/202104275003.aspx); [(2)] (https://www.cna.com.tw/news/firstnews/201812165002.aspx); [新世紀智庫論壇("Taiwan New Century Think Tank Forum")(Chinese)] (http://www.taiwanncf.org.tw/ttforum/81/81-04.pdf); [台灣民間真相與和解促進會("Taiwan Association for Truth and Reconciliation")(Chinese)] (https://taiwantrc.org/taiwan-history/white-terror-history/)