You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Korean_War

Context:
During World War II, Japan used Korea's food, livestock, and metals for their war effort. Japanese forces in Korea increased from 46,000 soldiers in 1941 to 300,000 in 1945. Japanese Korea conscripted 2.6 million forced laborers controlled with a collaborationist Korean police force; some 723,000 people were sent to work in the overseas empire and in metropolitan Japan. By 1942, Korean men were being conscripted into the Imperial Japanese Army. By January 1945, Koreans made up 32% of Japan's labor force. At the end of the war, other world powers did not recognize Japanese rule in Korea and Taiwan.

Question:
Who did Japan collaborate with to help control the citizens of Korea?

Korean police force