The arena for military competition and conflict has expanded dangerously in the past few decades. Wars used to be waged on relatively small areas of land and sea. World War I, fought mainly in Western Europe, involved combat aircraft and military airspace for the first time.
World War II, ending in 1945, started in Europe, spread to Asia and became global in its reach and effects. This extended impact of warfare was intensified in the Cold War by nuclear weapons. Space became a frontier for potential inter-state conflict after the Soviet Union launched the first artificial satellite in 1957, and both the Soviet Union and the United States later tested weapons that could destroy or disable satellites used for communications and other critical purposes.
The latest realm for espionage and unleashing new weapons is cyberspace, the largely invisible web of interconnected computer and information networks that form the operational fibers of advanced economies and their defense forces. Relations between China and the U.S. and its allies, strained by military rivalries and maritime disputes in the Asia-Pacific region, are also grating in cyberspace.