Question: Why did China need to resettle people in to the city the Chinese capitol was relocated during the Japanese occupation on 20th century?

full_context: Document 1: Sichuan: The Three Gorges Dam, the largest dam ever constructed, is being built on the Yangtze River in nearby Hubei province to control flooding in the Sichuan Basin, neighboring Yunnan province, and downstream. The plan is hailed by some as China's efforts to shift towards alternative energy sources and to further develop its industrial and commercial bases, but others have criticised it for its potentially harmful effects, such as massive resettlement of residents in the reservoir areas, loss of archeological sites, and ecological damages.
Document 2: Nanjing: A few days before the fall of the city, the National Government of China was relocated to the southwestern city Chungking (Chongqing) and resumed Chinese resistance. In 1940, a Japanese-collaborationist government known as the "Nanjing Regime" or "Reorganized National Government of China" led by Wang Jingwei was established in Nanjing as a rival to Chiang Kai-shek's government in Chongqing. In 1946, after the Surrender of Japan, the KMT relocated its central government back to Nanjing.
Document 3: Nanjing: On 21 April, Communist forces crossed the Yangtze River. On April 23, 1949, the Communist People's Liberation Army (PLA) captured Nanjing. The KMT government retreated to Canton (Guangzhou) until October 15, Chongqing until November 25, and then Chengdu before retreating to Taiwan on December 10. By late 1949, the PLA was pursuing remnants of KMT forces southwards in southern China, and only Tibet was left. After the establishment of the People's Republic of China in October 1949, Nanjing was initially a province-level municipality, but it was soon merged into Jiangsu province and again became the provincial capital by replacing Zhenjiang which was transferred in 1928, and retains that status to this day.
Document 4: Sichuan: In the 20th century, as Beijing, Shanghai, Nanjing, and Wuhan had all been occupied by the Japanese during the Second Sino-Japanese War, the capital of the Republic of China had been temporary relocated to Chongqing, then a major city in Sichuan. An enduring legacy of this move is that nearby inland provinces, such as Shaanxi, Gansu, and Guizhou, which previously never had modern Western-style universities, began to be developed in this regard. The difficulty of accessing the region overland from the eastern part of China and the foggy climate hindering the accuracy of Japanese bombing of the Sichuan Basin, made the region the stronghold of Chiang Kai-Shek's Kuomintang government during 1938-45, and led to the Bombing of Chongqing.
Document 5: Sichuan: Sichuan consists of two geographically very distinct parts. The eastern part of the province is mostly within the fertile Sichuan basin (which is shared by Sichuan with Chongqing Municipality). The western Sichuan consists of the numerous mountain ranges forming the easternmost part of the Qinghai-Tibet Plateau, which are known generically as Hengduan Mountains. One of these ranges, Daxue Mountains, contains the highest point of the province Gongga Shan, at 7,556 metres (24,790 ft) above sea level.
Document 6: Nanjing: In 1927, the Kuomintang (KMT; Nationalist Party) under Generalissimo Chiang Kai-shek again established Nanjing as the capital of the Republic of China, and this became internationally recognized once KMT forces took Beijing in 1928. The following decade is known as the Nanking decade.
Document 7: Sichuan: In the middle of the 17th century, the peasant rebel leader Zhang Xianzhong (1606–1646) from Yan'an, Shanxi Province, nicknamed Yellow Tiger, led his peasant troop from north China to the south, and conquered Sichuan. Upon capturing it, he declared himself emperor of the Daxi Dynasty (大西王朝). In response to the resistance from local elites, he massacred a large native population. As a result of the massacre as well as years of turmoil during the Ming-Qing transition, the population of Sichuan fell sharply, requiring a massive resettlement of people from the neighboring Huguang Province (modern Hubei and Hunan) and other provinces during the Qing dynasty.
Document 8: Sichuan: Sichuan was China's most populous province before Chongqing became a directly-controlled municipality; it is currently the fourth most populous, after Guangdong, Shandong and Henan. As of 1832, Sichuan was the most populous of the 18 provinces in China, with an estimated population at that time of 21 million. It was the third most populous sub-national entity in the world, after Uttar Pradesh, India and the Russian Soviet Federative Socialist Republic until 1991, when the Soviet Union was dissolved. It is also one of the only six to ever reach 100 million people (Uttar Pradesh, Russian RSFSR, Maharashtra, Sichuan, Bihar and Punjab). It is currently 10th.
Document 9: Nanjing: Nanjing, one of the nation's most important cities for over a thousand years, is recognized as one of the Four Great Ancient Capitals of China, and had been the world's largest city aggregately for hundreds of years, enjoyed peace and prosperity and beared wars and disasters. Nanjing served as the capital of Eastern Wu, one of the three major states in the Three Kingdoms period (211-280); the Eastern Jin and each of the Southern Dynasties (Liu Song, Southern Qi, Liang and Chen), which successively ruled southern China from 317-589; the Southern Tang, one of the Ten Kingdoms (937-76); the Ming dynasty when, for the first time, all of China was ruled from the city (1368-1421); and the Republic of China (1927–37, 1945–49) prior to its flight to Taiwan during the Chinese Civil War. The city also served as the seat of the rebel Taiping Heavenly Kingdom (1851–64) and the Japanese puppet regime of Wang Jingwei (1940–45) during the Second Sino-Japanese War, and suffered appalling atrocities in both conflicts, including the Nanjing Massacre. It has been serving as the capital city of Jiangsu province after the China was established, and is still the nominal capital of Republic of China that accommodates many of its important heritage sites, including the Presidential Palace and Sun Yat-sen Mausoleum. Nanjing is famous for human historical landscapes, mountains and waters such as Fuzimiao, Ming Palace, Chaotian Palace, Porcelain Tower, Drum Tower, Stone City, City Wall, Qinhuai River, Xuanwu Lake and Purple Mountain. Key cultural facilities include Nanjing Library, Nanjing Museum and Art Museum.
Document 10: Sichuan: The majority of the province's population is Han Chinese, who are found scattered throughout the region with the exception of the far western areas. Thus, significant minorities of Tibetan, Yi, Qiang and Nakhi people reside in the western portion that are impacted by inclement weather and natural disasters, environmentally fragile, and impoverished. Sichuan's capital of Chengdu is home to a large community of Tibetans, with 30,000 permanent Tibetan residents and up to 200,000 Tibetan floating population. The Eastern Lipo, included with either the Yi or the Lisu people, as well as the A-Hmao, also are among the ethnic groups of the provinces.
Document 11: Sichuan: From 1955 until 1997 Sichuan had been China's most populous province, hitting 100 million mark shortly after the 1982 census figure of 99,730,000. This changed in 1997 when the Sub-provincial city of Chongqing as well as the three surrounding prefectures of Fuling, Wanxian, and Qianjiang were split off into the new Chongqing Municipality. The new municipality was formed to spearhead China's effort to economically develop its western provinces, as well as to coordinate the resettlement of residents from the reservoir areas of the Three Gorges Dam project.
Document 12: Sichuan: Sichuan has been historically known as the "Province of Abundance". It is one of the major agricultural production bases of China. Grain, including rice and wheat, is the major product with output that ranked first in China in 1999. Commercial crops include citrus fruits, sugar cane, sweet potatoes, peaches and grapes. Sichuan also had the largest output of pork among all the provinces and the second largest output of silkworm cocoons in 1999. Sichuan is rich in mineral resources. It has more than 132 kinds of proven underground mineral resources including vanadium, titanium, and lithium being the largest in China. The Panxi region alone possesses 13.3% of the reserves of iron, 93% of titanium, 69% of vanadium, and 83% of the cobalt of the whole country. Sichuan also possesses China's largest proven natural gas reserves, the majority of which is transported to more developed eastern regions.
Document 13: Modern history: Few Chinese had any illusions about Japanese designs on China. Hungry for raw materials and pressed by a growing population, Japan initiated the seizure of Manchuria in September 1931 and established ex-Qing emperor Puyi as head of the puppet state of Manchukuo in 1932. During the Sino-Japanese War (1937–1945), the loss of Manchuria, and its vast potential for industrial development and war industries, was a blow to the Kuomintang economy. The League of Nations, established at the end of World War I, was unable to act in the face of the Japanese defiance. After 1940, conflicts between the Kuomintang and Communists became more frequent in the areas not under Japanese control. The Communists expanded their influence wherever opportunities presented themselves through mass organizations, administrative reforms, and the land- and tax-reform measures favoring the peasants—while the Kuomintang attempted to neutralize the spread of Communist influence.
Document 14: Pacific War: The war entered a new phase with the unprecedented defeat of the Japanese at Battle of Suixian-Zaoyang and 1st Battle of Changsha. After these victories, Chinese nationalist forces launched a large-scale counter-offensive in early 1940; however, due to its low military-industrial capacity, it was repulsed by Japanese army in late March 1940. In August of 1940, Chinese communists launched an offensive in Central China; in retaliation, Japan instituted the "Three Alls Policy" ("Kill all, Burn all, Loot all") in occupied areas to reduce human and material resources for the communists. By 1941 the conflict had become a stalemate. Although Japan had occupied much of northern, central, and coastal China, the Nationalist Government had retreated to the interior with a provisional capital set up at Chungking while the Chinese communists remained in control of base areas in Shaanxi. In addition, Japanese control of northern and central China was somewhat tenuous, in that Japan was usually able to control railroads and the major cities ("points and lines"), but did not have a major military or administrative presence in the vast Chinese countryside. The Japanese found its aggression against the retreating and regrouping Chinese army was stalled by the mountainous terrain in southwestern China while the Communists organised widespread guerrilla and saboteur activities in northern and eastern China behind the Japanese front line.
Document 15: Sichuan: Sichuan came under the firm control of a Chinese central government during the Sui dynasty, but it was during the subsequent Tang dynasty where Sichuan regained its previous political and cultural prominence for which it was known during the Han. Chengdu became nationally known as a supplier of armies and the home of Du Fu, who is sometimes called China's greatest poet. During the An Lushan Rebellion (755-763), Emperor Xuanzong of Tang fled from Chang'an to Sichuan. The region was torn by constant warfare and economic distress as it was besieged by the Tibetan Empire.
ground_truth: the Three Gorges Dam project.
sub_queries: To which city was the Chinese capitol relocated to during Japanese occupation in the 20th century? Answer: Chongqing
Why did China need to resettle people into Chongqing ? Answer: the Three Gorges Dam project.