In what year did Japan sign the Treaty of Mutual Cooperation and Security with the United States?

The Treaty of Mutual Cooperation and Security between the United States and Japan Nihon-koku to Amerika-gasshūkoku to no Aida no Sōgo Kyōryoku oyobi Anzen Hoshō Jōyaku), also known in Japan as Anpo jōyaku or just Anpo for short, was first signed in 1951 at the San Francisco Presidio following the signing of the Treaty of San Francisco (commonly known as the Peace Treaty of San Francisco) at the San Francisco War Memorial Opera House. Then, the Security Treaty was later amended further on January 1960 between the US and Japan in Washington.

When the Treaty was first signed, it contained provisions that permitted the United States to act for the sake of maintaining peace in East Asia and even exert its power on Japanese domestic quarrels. The latter part mentioned has been deleted in the revised version of the treaty. In the amended treaty, articles that delineate mutual defense obligations, the US obligations to pre-inform Japan in times of the US army mobilization were included to alleviate unequal status suggested in the treaty signed in 1952.

The treaty established that any attack against Japan or the United States perpetrated within Japanese territorial administration would be dangerous to the respective countries' own peace and safety. It requires both countries to act to meet the common danger. To support that requirement, it provided for the continued presence of US military bases in Japan.