Japanese Colonial Period (1910–1945)

Korea’s annexation by the Japanese Empire in 1910 and its occupation until 1945 was a watershed in Korean history and in the shaping of the ideology and grievances that would define the Democratic People’s Republic of Korea. The 35-year colonial period saw the systematic integration of the Korean peninsula into the Japanese imperial project, the suppression of Korean identity and autonomy, nationalist resistance, and the accumulation of historical trauma that the DPRK has weaponized as justification for its autarkic posture and anti-Western ideology.

Background: Korea Before Annexation

At the turn of the twentieth century, Korea (the Joseon Dynasty, renamed the Daehan Empire in 1897) was a weakened state caught between competing imperial powers — Japan, China, and Russia. The Sino-Japanese War (1894–1895) and the Russo-Japanese War (1904–1905) resolved this competition in Japan’s favor. By the 1905 Treaty of Portsmouth (brokered by U.S. President Theodore Roosevelt), Russia recognized Japan’s paramount interests in Korea. The 1905 Eulsa Treaty converted Korea into a Japanese protectorate, and the 1907 Hague Convention protest by Emperor Gojong’s envoys failed to attract international support.

Ito Hirobumi, the Japanese Resident-General, was the key architect of protectorate policy until his assassination on October 26, 1909 at Harbin Station by the Korean nationalist An Jung-geun — an act celebrated in Korean nationalist memory and, particularly, in the DPRK. The assassination failed to halt annexation. The August 22, 1910 Treaty of Annexation formally incorporated Korea into the Japanese Empire.

Colonial Administration and Integration

The Japanese established a Governor-General system headquartered in Seoul (which they renamed Gyeongseong/Keijō), replacing Korean royal authority with direct imperial administration. The colony was reorganized into thirteen provinces and integrated into the Japanese economic sphere. The colonial period involved two distinct administrative phases:

The Military Phase (1910–1919): Characterized by harsh military rule, suppression of any Korean political activity, and the systematic dismantling of pre-existing Korean institutions. Japanese gendarmes (Kempeitai) exercised police functions alongside the regular colonial police. Land surveys conducted between 1910 and 1918 dispossessed many Korean smallholders, with approximately 40% of arable land transferred to Japanese ownership or state control.

The Cultural Policy Phase (1919–1931): Following the 1919 independence movement, the colonial administration shifted to a nominally more conciliatory “Cultural Policy” (bunka seiji), relaxing some press restrictions and permitting limited Korean cultural expression. In practice, surveillance and repression continued; Korean-language newspapers (Dong-a Ilbo, Joseon Ilbo) were permitted but subject to censorship.

The Wartime Mobilization Phase (1931–1945): After Japan’s 1931 invasion of Manchuria and especially after 1937 (full-scale war with China), colonial policy turned sharply toward assimilation and extraction. The peninsula was militarized heavily and its population mobilized for the war effort.

The colonial population was substantial: Korea had approximately 13 million inhabitants at annexation in 1910, growing to approximately 25 million by 1944, reflecting both natural growth and some immigration of ethnic Koreans from Manchuria.

Industrial Development and Unequal Geography

Colonial infrastructure was designed for extraction and military use rather than Korean development, but it nonetheless substantially transformed the peninsula. The Japanese built approximately 6,000 kilometers of railway by 1945 (primarily along north-south axes to move goods to ports), expanded the road network, and developed harbor facilities at Busan, Incheon, Wonsan, and Nampho.

Crucially, heavy industry was concentrated in the north, near Manchuria and China. Japanese capital developed the region’s coal and iron ore deposits (particularly in South Hamgyong Province, around Hamhung and Chongjin), hydroelectric power (the massive Suiho Dam on the Yalu River, completed in 1943, with 700 MW capacity), and chemical industries. The Hungnam nitrogen fertilizer plant (later the Hamhung chemical complex), built by Noguchi Shitagau’s Nitchitsu company beginning in 1927, was one of Asia’s largest chemical plants and would later become the nucleus of the DPRK’s industrial base.

By contrast, light industry, commerce, and consumption were concentrated in the south. This geographic division — heavy industry and resources in the north, light industry and agriculture in the south — would prove consequential when the 38th parallel partition imposed in August 1945 divided the peninsula along roughly this industrial line.

Pyongyang, the future DPRK capital, developed substantially under colonial rule, growing from a regional center to a city of approximately 300,000 by 1945, with Japanese investment in rail connections, industry, and urban infrastructure. Kaesong, a historic capital of the Goryeo dynasty, served as an administrative center near the geographic heart of the peninsula.

Cultural Suppression and Assimilation Policy

The Japanese regime pursued an explicit assimilation (naisen ittai — “Japan and Korea as one body”) policy aimed at erasing Korean identity in favor of Japanese imperial subjecthood. Key aspects included:

Language suppression: Korean language was gradually eliminated from schools and public life, replaced by Japanese. After 1938, Japanese-only education was mandated; by the early 1940s, Korean was effectively banned from official use. The near-total replacement of Korean with Japanese in urban commercial and administrative life within a generation constituted a profound cultural rupture.

Religious control: Christian and Buddhist institutions were subordinated to Japanese Shinto nationalism. Koreans were pressured to participate in Shinto shrine worship — mandatory shrine visits were required at schools and workplaces. This caused particular friction with Korean Christians, who by 1945 numbered approximately 300,000 (predominantly Presbyterian and Methodist). Christian resistance to shrine worship generated significant confrontations; some Korean clergy were imprisoned for refusing to comply.

Name assimilation (Sōshi-kaimei): From 1940, Koreans were encouraged and increasingly coerced to adopt Japanese names. By 1944, approximately 80% of Korean households had registered Japanese-style names, though this formal compliance often coexisted with continued private use of Korean names.

Historical revisionism: Korean history was reframed within a Japanese imperial narrative, with Korea portrayed as culturally inferior and historically dependent on China — and therefore in need of Japanese “guidance.” School curricula presented the annexation as a voluntary modernization rather than a conquest.

Korean Nationalist Resistance

Korean nationalism, suppressed by Japanese police and military, took multiple forms:

Armed resistance: Korean armed groups and guerrilla forces operated primarily in Manchuria and Russian territory. An Jung-geun’s 1909 assassination of Ito Hirobumi was the most dramatic pre-annexation act. During the colonial period, independence armies (Dongnipgun) operated from Manchurian bases, conducting cross-border raids and maintaining an underground presence. Yi Pom-sok (later a South Korean defense minister) commanded one such force. The scale was limited and the Japanese suppressed them ruthlessly.

The March 1st Independence Movement (1919): On March 1, 1919, coordinated protests erupted across Korea following the death of Emperor Gojong, inspired partly by U.S. President Woodrow Wilson’s Fourteen Points and the principle of national self-determination. Thirty-three nationalist leaders signed and read aloud a Declaration of Independence at a Seoul restaurant (Taehwagwan) before being arrested. Mass demonstrations spread across the peninsula over the following weeks. Japanese military and police responses were severe: Korean estimates place the number killed at approximately 7,500 and arrested at 45,000 over the course of the protest period; Japanese official records reported 553 killed and 12,000 arrested. The colonial administration burned the village of Jeam-ri (April 1919) with Christian residents locked inside, a massacre that became emblematic of colonial brutality. The March 1st Movement, though ultimately suppressed, became the foundational symbol of Korean resistance and is celebrated annually in both North and South Korea (Samil-jeol).

Exile and underground networks: Korean nationalists fled to China, Russia, and Manchuria, establishing government-in-exile councils and resistance networks. The Korean Provisional Government, established in Shanghai in April 1919 under Syngman Rhee (later South Korea’s first president), represented the constitutional nationalist strand. These exiles included socialists, anarchists, conservatives, and religious nationalists — factions that would later reconstitute themselves as the rival blocs of the Cold War division.

Non-violent protest and cultural resistance: Korean intellectuals, writers, and activists engaged in literature, journalism, and cultural production as forms of coded resistance. The movement known as the “Cultural Nationalists” promoted Korean language preservation, historical scholarship, and economic self-strengthening (the “Buy Korean goods” campaign).

Communist and Socialist Movements

Socialist and communist ideas entered Korea from Russian and Chinese revolutionary currents. A Korean Communist Party was founded in April 1925 (in Seoul), though it remained fragmented, repeatedly dissolved by Japanese police, and dominated by factional disputes between Moscow-aligned and Shanghai-aligned groups. Korean communists operated primarily underground or in exile, in Manchuria, China, and the Soviet Far East.

Among those operating in Manchuria in the 1930s was Kim Sŏng-ju (b. 1912), who adopted the nom de guerre Kim Il-sung. Between approximately 1932 and 1940, Kim commanded a unit of the anti-Japanese People’s Revolutionary Army in Manchuria, conducting guerrilla operations against Japanese forces in the area around Jilin Province. Japanese military records confirm that a guerrilla leader called “Kim Il-sung” participated in a June 1937 raid on Poch’onbo (on the Korean-Manchurian border), a minor engagement that was nonetheless publicized in Korean newspapers and established his name in the public consciousness.

By 1940–1941, under sustained Japanese counter-guerrilla pressure, Kim’s unit was decimated and he retreated to Soviet territory, where he was integrated into the Soviet 88th Special Reconnaissance Brigade, a multinational unit of Korean and Chinese guerrilla remnants. He spent 1941–1945 in the USSR, training at Khabarovsk and attaining the rank of major in the Red Army. This period in Soviet service — not his guerrilla activities — is what positioned him for Soviet selection as Korea’s post-liberation leader.

The DPRK would later mythologize Kim’s Manchurian resistance into a heroic 15-year armed struggle that “defeated Japanese imperialism” — an exaggeration, but one built on a documented kernel of actual guerrilla activity. The legitimizing narrative of anti-Japanese resistance became foundational to the DPRK’s state ideology and propaganda, particularly the identification of Mount Paektu with Kim Il-sung’s guerrilla struggles.

Wartime Mobilization: Forced Labor and Sexual Slavery

As Japan’s position deteriorated in World War II (particularly after 1942–1943), the colonial regime intensified Korea’s mobilization. Approximately 700,000 Korean men were conscripted or drafted into the Japanese military and labor corps between 1939 and 1945, serving in theaters across the Pacific and Asia. An additional 1–2 million Koreans were mobilized as civilian labor (forced labor for mines, factories, and construction), both in Korea and in Japan.

A distinctive and contested wartime institution was the “comfort women” (ianfu) system — the conscription and coercion of women into sexual slavery for the Japanese military. Estimates of the number of Korean women subjected to this system range from 50,000 to 200,000 (the wide range reflects contested definitions and incomplete records). The women, recruited by brokers with false promises of factory work or nursing, were transported to military “comfort stations” across Asia. Survivors who came forward in the 1990s — the “halmeoni” (grandmother) movement — triggered a sustained historical and diplomatic controversy. Japan issued a partial acknowledgment in the 1993 Kono Statement; a 2015 bilateral agreement between Japan and South Korea (which provided ¥1 billion for a foundation supporting survivors) was later rejected by survivors and South Korean civil society as insufficient.

In the north, the militarization of the peninsula was particularly intense along the Manchurian border and in coastal areas, as Japanese planners prepared for an anticipated U.S. invasion from the north. Soviet forces entering Korea in August 1945 encountered substantial Japanese fortifications.

The Korean Diaspora: Japan, Manchuria, and the Soviet Far East

Colonial rule generated large Korean diasporas whose descendants would shape the Cold War dynamics of Northeast Asia. By 1945, approximately 2 million Koreans lived in Japan (Zainichi Koreans), many having arrived as wartime labor conscripts or economic migrants. Most remained in Japan after liberation; their descendants (estimated at 500,000–600,000 today) occupy a legally distinctive position as permanent residents, subject to historical discrimination and ongoing debates over citizenship rights.

Approximately 1.5–2 million Koreans lived in Manchuria, many as agricultural settlers, guerrillas, or industrial workers. These Manchurian Koreans (Joseonjok) became the foundation of the Chinese Korean autonomous region in Yanbian after 1949 and are today the community through which Sino-DPRK border trade and defector networks operate.

Soviet Koreans (Koryo-saram) — numbering approximately 180,000 in 1937, before Stalin deported the entire population to Central Asia — occupied a tragic position: used as intelligence assets, then collectively punished as potential Japanese spies.

The End of Colonial Rule: August 1945 and Partition

Japan’s surrender on August 15, 1945 (Liberation Day, or Gwangbokjeol — celebrated as a national holiday in both Koreas) left the peninsula in a strategic vacuum. On August 10–11, 1945, two American colonels (Dean Rusk, later Secretary of State, and Charles Bonesteel) drew a line at the 38th parallel as a proposed administrative division, chosen hastily from a National Geographic map as a compromise between Soviet and American occupation zones. The Soviets accepted this line.

Soviet forces entered the north in August 1945 and rapidly occupied the territory above the 38th parallel, installing Korean communist cadres (including Kim Il-sung, returned from Soviet service) in administrative positions. American forces landed in the south in September 1945, finding a more complex political landscape including multiple political factions, the Korean Provisional Government, and a spontaneous leftist People’s Republic that was quickly suppressed.

The 38th parallel partition, intended as a temporary administrative measure, became permanent — the foundation of a Cold War division that the Korean War (1950–1953) hardened into the modern inter-Korean border.

Legacy and Historical Interpretation

The Japanese colonial period left deep and lasting marks:

Material transformation: The colonial period built infrastructure and heavy industry — particularly in the north — that the DPRK would inherit and that formed the basis of its early industrial capacity. The chemical and metallurgical industries of Hamhung, the hydroelectric power of the Yalu River, and the railway networks were built on colonial foundations.

Social dislocation: Millions of Koreans were displaced, uprooted, or separated by the 1945 partition and the subsequent Korean War. Families were divided across the 38th parallel; reunions have been rare and politically fraught.

Historical memory and the DPRK founding narrative: The colonial experience became a permanent reference point in Korean nationalism. The DPRK weaponized anti-Japanese and anti-imperialist rhetoric as core legitimizing ideology, framing juche (self-reliance) as a direct reaction against historical domination by Japan — and, by extension, Japan’s American ally. Kim Il-sung’s mythologized anti-Japanese resistance became the founding act of the DPRK’s legitimacy claim.

The comfort women controversy: This remains a major fault line in Japan–South Korea relations and, by extension, in U.S. alliance management in Northeast Asia. The DPRK uses it rhetorically but has its own historical complications regarding wartime collaboration by some Korean elites with the colonial administration.

Strategic legacy: The Soviet occupation of the north and the American occupation of the south, followed by partition, were direct products of the war’s conclusion and Japan’s collapse. Without the colonial period and World War II, the division of Korea — and therefore the DPRK itself — would not have occurred.

The experience of Japanese colonialism thus shaped the DPRK’s foundational ideology: deep skepticism of foreign powers, commitment to national independence, emphasis on military strength and autarky, and a victim narrative that justified the regime’s grip on power as necessary defense against historical repetition.

Related

• Korean War — the war that hardened the 1945 partition into the permanent inter-Korean border
• Kim Il-sung — the anti-Japanese guerrilla whose colonial-era struggle became the DPRK founding myth
• Government Structure — the state that inherited the colonial administrative and industrial base
• State Ideology and Propaganda — juche and the anti-imperialist narrative rooted in the colonial experience
• Nuclear Weapons Program — the autarkic security posture descended from the colonial victim narrative
• Hamhung — the chemical-industrial city built on the colonial Hungnam complex
• Pyongyang — the capital that expanded under colonial rail and industrial investment
• Kaesong — the historic Goryeo capital administered from the peninsula’s center under the colony
• Mount Paektu — the sacred mountain tied to Kim Il-sung’s mythologized guerrilla campaign
• Wonsan — a colonial-era treaty port and site of the 1929 Wonsan General Strike
• Sino–North Korean Relations — the Manchurian era of Korean–Chinese communist cooperation that preceded the alliance
• Partition and Founding (1945–1948) — the 1945 liberation and 38th-parallel partition that immediately followed colonial rule