World War II: Philippine Commonwealth troops under the Philippine Commonwealth Army units enter the province of Ilocos Sur in Northern Luzon and attack invading Japanese Imperial forces.

The Commonwealth of the Philippines was an unincorporated territory and commonwealth of the United States that existed from 1935 to 1946. It was established following the Tydings–McDuffie Act to replace the Insular Government of the Philippine Islands and was designed as a transitional administration in preparation for full Philippine independence. Its foreign affairs remained managed by the United States.

The Imperial Japanese Army was the principal ground force of the Empire of Japan from 1871 to 1945. It played a central role in Japan’s rapid modernization during the Meiji period, fought in numerous conflicts including the First Sino-Japanese War, the Russo-Japanese War, World War I, the Second Sino-Japanese War, and World War II, and became a dominant force in Japanese politics. Initially formed from domain armies after the Meiji Restoration, it evolved into a powerful modern military influenced by French and German models. The IJA was responsible for several overseas military campaigns, including the invasion of Manchuria, involvement in the Boxer Rebellion, and fighting across the Asia-Pacific during the Pacific War. Notorious for committing widespread war crimes, the army was dissolved after Japan's surrender in 1945, and its functions were succeeded by the Japan Ground Self-Defense Force.

January 8 is the eighth day of the year in the Gregorian calendar; 357 days remain until the end of the year.