The Quadrilateral Security Dialogue (QSD) is an informal strategic dialogue between the United States, Japan, Australia and India that is maintained by talks between member countries. The dialogue was initiated in 2007 by Prime Minister Shinzo Abe of Japan.

The quadrilateral grouping had first met in 2007, it was unable to sustain momentum as China expressed concerns about what it saw as an attempt at containment by like-minded democracies in the Asia-Pacific.

The QSD ceased following the withdrawal of Australia during Kevin Rudd’s tenure as prime minister, reflecting ambivalence in Australian policy over the growing tension between the United States and China in the Asia-Pacific.

However, during the 2017 ASEAN Summits in Manila (on the sidelines of the Association of Southeast Asian Nations and East Asia Summits) all four former members rejoined in negotiations to revive the quadrilateral alliance.

Convened around the theme of a “free and open Indo-Pacific,” the first quadrilateral meeting addressed seven core themes: the rules-based order in Asia, freedom of navigation and overflight in the maritime commons, respect for international law, enhancing connectivity, maritime security, the North Korean threat and nonproliferation, and terrorism.

Source: Wikipedia & The Diplomat