Timor-Leste had been colonized by Portugal since the 16th century. In 1974, Portugal abandoned its sovereignty over Timor-Leste, but it was followed by the annexation by Indonesia in 1976. Armed violence occurred between pro-independence and pro-Indonesia militias after the annexation, but finally the peace agreement was concluded in 1999.

On May 20, 2002, after a Constituent Assembly election in August 2001 and a presidential election in April 2002, East Timor gained its independence, becoming the first nation to do so in the twenty-first century. The country is now in the process of establishing itself as an independent state.

In the course of these developments, the UN Mission in East Timor (UNAMET), the UN Transitional Administration in East Timor (UNTAET), and the UN Mission of Support in East Timor (UNMISET) have played key roles. In addition, due to the deterioration in the security situation from April 2006, the UN Integrated Mission in Timor-Leste (UNMIT) was established in August of the same year.

Japan has sent a total of some 3,400 personnel to East Timor and other places in an international peace cooperation assignment to assist the UN activities.