It is a historical thing, and a lot of people don't even know that phrase exists today. The reason why Westerners called the Chinese the 'Sick Man of Asia' was because of how unstable their country was when the Europeans traded with them in the 1800's during the late Qing Dynasty. China had a horrible economy, a military that was not modernized, constant civil wars, warlords, unequal trade with other countries, and of course political chaos. At the same time, Europeans admired Japan because the Japanese had a modernized army and navy, a great economy, and were willing to trade with the Europeans and make treaties while remaining an isolated culture at the same time. This stayed true about Japan, in relation to China, up until about 10 years ago. Basically, in the old days, China had more bullshit happening in their country than other Asian powers such as Thailand, Burma, and also British India. They were kind of like that country that always fought foreigners like patriots, but fought themselves even more. It was hard for China to get their country stable until Sun Yat Sen overthrew the Qing Empire and created the first Chinese republic... which was overthrown by communists 40 years later, but by then, the term was no longer widely known and they were simply known as 'commies' during the Cold War. And today, its just not used at all or even known.
great post but completely unnecessary, raiseofnegrito is a viet troll who's jealous of chinese achievements LOL