The territory of country cannot be eternal, therefore territory of country is constantly changing. From ancient times to present day, China has never had same territory in any two eras. Over thousands of years of history, some areas have been lost and some have been added. So which areas that once belonged to China and were eventually lost are most regrettable?
First of all, it should be said about Outer Northeast. The so-called outer northeast refers to northeastern region ceded to Russia by Qing Dynasty after Second Opium War, including 600,000 square kilometers south of Outer Mountains of Xinan, north of Heilongjiang, and 400,000 square kilometers east of Ussuri River. , including Sakhalin Island, mln sq. km, with a total area of 1 million sq. km. The outer northeast is not only large in size, but also has a high land value. The natural environment here is similar to Jilin and Heilongjiang, with relatively abundant rainfall and extensive black land. If outer northeast is not lost, China will basically have full basin of Heilongjiang River and expand area of North Datsang. "In addition, with Outer Northeast, Northeast region will have Sea of Okhotsk (North Sea) and Sea of Japan coastline, and problem of mouth of Northeast region will be solved. The shipping cost in Heilongjiang area will be greatly improved.
North Vietnam should be in second place. The ancient city of "Jiaozhi" in northern Vietnam, after Qin dynasty destroyed Baiyue, founded Xiang district, and Han dynasty divided it into three districts: Jiaozhi, Jiuzhen and Rinan. Later it was also called Jiaozhou. From Han Dynasty to Tang Dynasty, Jiaozhi belonged to territory of China, and Tang Dynasty also established Annan protectorate here. However, during Five Dynasties and Ten Kingdoms period, Vietnam seceded from Southern Han regime and gradually moved towards independence. During Northern Song Dynasty, Vietnam defeated Song Dynasty army, and Song Dynasty was forced to recognize independence of Vietnam. After that, Vietnam became officially an independent country. North Vietnam has Red River Plain suitable for farming. If we are here, we will have more advantages in South China Sea and Southeast Asia.
Third place - North Korea. The North Korea mentioned here refers to northern part of Korean peninsula. The earliest regimes here - Jizi Joseon, Wiman Joseon and Goguryeo were created by ethnic groups of Northeast China. During Han Dynasty, four Han counties were established in North Korea, which were gradually annexed by Goguryeo. After Tang Dynasty destroyed Goguryeo, it was first able to control North Korea, and then Silla (South Korea) moved north and gradually forced Tang Dynasty out of Korean Peninsula. However, northern border of Korea at that time had not yet reached Yalu River and Tumen River. At beginning of Ming Dynasty, Goryeo Dynasty of Korea seized opportunity to move north, pushing its territory to Yalu and Tumen rivers, and Ming Dynasty had nothing to do with this. Not only that, Zhu Yuanzhang also bestowed title of "North Korea" on South Korean Li Dynasty. Due to advance of South Korea to north, outlets to the sea in Northeast China were compressed.
The fourth place should be Ryukyu Islands. Initially, Ryukyu was not in China, but was a vassal state during Ming and Qing dynasties. However, at a meeting in Cairo, Roosevelt asked Chiang Kai-shek to take over Ryukyu Islands, but Chiang Kai-shek refused. The United States later decided to administer Ryukyu Islands itself, and later transferred them to Japan, which is now Okinawa Prefecture. If Ryukyu belonged to China, then there would be no dispute in East China Sea between China and Japan, let alone problem of Diaoyu Islands, and second island chain of United States would also open its mouth. China goes directly to Pacific Ocean.
The fourth location is outer northwest. The outer northwest is land allocated to Russia by Qing dynasty in 1960s, covering an area of 440,000 square kilometers, most of which is now owned by Kazakhstan and other countries. Most of these lands are deserts and Gobi, with exception of Yili river basin. The Ili River Basin is wettest place in Northwest China, with 600 millimeters of rainfall on windward slope, Ili River is also very full of water and finally flows into Lake Balkhash. In ancient times, this place has always been an important economic center in Northwest, during Han Dynasty, largest kingdom of Wusong in Western regions was located here. It is a pity that this generation was delayed. Fortunately, upper reaches of Ili River valley were conquered by Zuo Zongtang, Zeng Jize and others.
The fifth region is Outer Mongolia. The area of Outer Mongolia reaches 1.56 million square kilometers, and with Tannu Wulyankhai area, it can reach 1.7 million square kilometers. It's a pity that Outer Mongolia became independent after intervention of Soviet Union after World War II. With Outer Mongolia, China's northern border will be much smaller, but territory controlled will increase significantly, and Beijing will gain space for defense. Although Mongolia has harsh natural conditions, it is rich in mineral resources, with over 2 billion tons of copper reserves, 3400 tons of gold reserves, 300 billion tons of coal reserves, 8 billion barrels of oil reserves, 2 billion tons of iron ore reserves, and fluorite. The deposit's reserves are 28 million tons, phosphorite reserves - 200 million tons, molybdenum ore reserves - 240,000 tons, zinc ore reserves - 60,000 tons, silver ore reserves - 7,000 tons. In addition, pastures of Outer Mongolia can provide a large amount of high quality meat suitable for development of pastoralism.