On this day, 26 years ago, April 23, 1999 (March 8, 1999, the lunar calendar), NATO commemorated its 50th anniversary and established a new alliance strategy. NATO summit held in Washington On April 23, 1999, the NATO summit opened at the Reagan International Trade Center in the United States. The main topics of the meeting were commemorating the 50th anniversary of the founding of NATO, the Kosovo crisis and meeting the security challenges of the 21st century. Heads of state and government from 19 NATO member states and 23 Partnership for Peace countries attended the meeting. Russia and Belarus refused to attend the meeting over protesting NATO air strikes on Yugoslavia. On April 24, a new Alliance Strategic Concept was adopted. This new NATO strategic document for the 21st century proposes that NATO will continue to adhere to the "collective defense" policy in the future, but at the same time respond to conflicts in its surrounding areas to ensure security in the Euro-Atlantic Alliance region. NATO has adopted a total of 65 strategic concepts, mainly including four contents: the alliance's goals and tasks, strategic outlook, ways to maintain security in the 21st century, and guiding principles for NATO's military forces. The document believes that the dangers of the Cold War no longer exist, but NATO still faces a "more challenging" prospect, with new opportunities and crises coexisting. Due to changes in the strategic environment, NATO is unlikely to suffer a large-scale invasion of conventional weapons, but this possibility still exists in the long run. NATO leaders emphasized that "safeguarding the freedom and security of all member states through political and military means" is NATO's "fundamental and lasting goal." They also stressed that NATO will also actively participate in crisis management and effectively prevent conflicts in the future. The document said that when NATO solves security issues in the 21st century, it will not only take military measures, but will also use "a wide range of means" in the political, economic, social and environmental fields to build a "European security building." This is the second document on strategic concepts proposed by NATO after the end of the Cold War. In 1991, NATO adopted its first strategic concept document at the Rome Summit.