Quadrilateral Security Dialogue

The Quadrilateral Security Dialogue (QSD), commonly known as the Quad, is a strategic security dialogue between Australia, India, Japan and the United States that is maintained by talks between member countries. The dialogue was initiated in 2007 by Japanese Prime Minister Shinzo Abe, with the support of Australian Prime Minister John Howard, Indian Prime Minister Manmohan Singh and U.S. Vice President Dick Cheney. The dialogue was paralleled by joint military exercises of an unprecedented scale, titled Exercise Malabar. The diplomatic and military arrangement was widely viewed as a response to increased Chinese economic and military power.

The Quad ceased in 2008 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 Indo-Pacific. Following Rudd's replacement by Julia Gillard in 2010, enhanced military cooperation between the United States and Australia was resumed, leading to the placement of U.S. Marines near Darwin, Australia, overlooking the Timor Sea and Lombok Strait. Meanwhile, India, Japan, and the United States continued to hold joint naval exercises under Malabar.

During the 2017 ASEAN Summits in Manila, all four former members led by Abe, Australian Prime Minister Malcolm Turnbull, Indian Prime Minister Narendra Modi, and US President Donald Trump agreed to revive the quadrilateral alliance in order to counter China militarily and diplomatically in the Indo-Pacific region, particularly in the South China Sea. Tensions between Quad members and China have led to fears of what was dubbed by some commentators "a new Cold War" in the region, and the Chinese government responded to the Quadrilateral dialogue by issuing formal diplomatic protests to its members, calling it "Asian NATO"; Indian Foreign Minister S. Jaishankar denies China's allegations and claimed India never had ‘NATO mentality’.

In a joint statement in March 2021, "The Spirit of the Quad," the Quad members described "a shared vision for a Free and Open Indo-Pacific," and a "rules-based maritime order in the East and South China seas," which the Quad members state are needed to counter Chinese maritime claims. The Quad pledged to respond to COVID-19, and held a first Quad Plus meeting that included representatives from South Korea, New Zealand, and Vietnam to work on its response to it. As of 2023, Quad countries together have a combined GDP nominal of US$36.7 trillion (34.7% of the gross world product) and a combined GDP PPP of US$48.1 trillion(27.5% of the world's GDP).