The ASEAN Treaty of Amity and Cooperation provides guidance for intra-ASEAN cooperation, as well as ASEAN engagement with external partners such as the United States and China. The principles of the treaty reflect the ASEAN members’ historical preferences and priorities for management of contentious issues. The treaty, concluded in 1976, was opened to accession by external states; China acceded in 2003, , and the United States did the same in 2009.