It means that the foreign ministers of the United States, Australia, Japan, and India held a summit in Tokyo recently, which was regarded by the outside world as forming a new line of defense against China. This Quartet Security Dialogue, also known as the "Quad", was actually born out of the "Asia's Democratic Security Diamond" proposed by former Japanese Prime Minister Shinzo Abe when he became prime minister for the second time in 2012.
For the first time, the Abe government proposed the so-called "value diplomacy", hoping to form an alliance with countries that also value photo background removing democracy, freedom, and human rights to jointly counter the expansion of China's power. This is a continuation of the "Arc of Freedom and Prosperity" proposed by Shinzo Abe when he first came to power, but it did not receive any attention at the time, leaving Japan alone. The reason why the diamond of Asian democracy and security was not taken seriously at the beginning was that the international atmosphere at that time was still very friendly to China. Although the United States had begun to propose the concept of "returning to the Asia-Pacific" in 2010, it was still only a policy oath at that time.
Australia and India have a very good relationship with Beijing and are making every effort to explore China's huge market. Unlike Japan, which is in East Asia and has a conflict of geographical interests with China, it has gradually felt the crisis of China's expansion. The Abe administration saw the United States' policy of returning to the Asia-Pacific region, and successively proposed the concept of the diamond of Asian democracy and security, but did not expect that the United States itself would not take a positive attitude. When Obama himself visited Western Pacific countries in 2011, he delivered a speech to the Australian Parliament, unveiling a policy platform for returning to the Asia-Pacific region. As a result, in the next four or five years, this policy was not really implemented due to various external reasons.