新闻背景：20多个国家和地区也有类似的区域（在线收听）

China's Air Defense Identification Zone is aimed at controlling and monitoring incoming aircraft, in the interest of national security. But China is definitely not alone.

Currently, more than 20 countries and regions have their own Air Defense Identification Zone.

The first was established by the US and Canada in 1950, when they jointly created a North American zone.

Japan’s air defense zone was set up by the US during its post-World War Two occupation of Japan. Since then, Japan has unilaterally expanded its zone twice, in 1972 and in 2010, pushing it further into the East China Sea. Japan’s Air Defense Identification Zone is now five times bigger than its national territory, extending as close as 100 nautical miles from China’s coastline.

China says Japan’s air defense zone is illegal, as it covers the Diaoyu Islands.

South Korea’s Air Defense Identification Zone was established in 1951 during the Korean War, also with the help of the US.

China’s newly launched defense zone overlaps with South Korea’s, and covers the Suyan Island, known as Ieodo in South Korea, a submerged rock claimed by Seoul.