*2.1. Overseas Research*

Rural development is the inevitable connotation of urbanization. Adam Smith, the originator of classical economics, put forward the "natural order". He believed that there were villages first and then cities; cities came from rural development, and the wealth and poverty of a country mainly depended on the historical geography, institutional culture and other elements of urban and rural development [10]. Influenced by this, the German economic geographer Von Thünen [11], regards urban and rural areas as a whole in his "isolated country" model and explores the law of spatial distribution for different industries between urban and rural areas.

Western urban research can be traced back to the ancient Greek city-state theory where the ancient Greek combined the construction of the city-state with politics and civilization [12,13]. Plato's utopia is the earliest utopia in human history [14]. The proponents of Utopia strongly advocate the integration and further design of urban and rural areas [15]. Subsequently, garden cities, urban agglomeration areas, organic evacuation and other theories also emphasize the integration of urban and rural development [16–19].

From 1940 to 1980, the "dual structure" paradigm dominated the study of urban–rural relations in the West. Due to the one-sided emphasis on urban and industrial development resulting in the development of rural agriculture lagging behind [20], the "dual structure" gave birth to two theoretical schools of urban and rural development. One is the Jorgenson model and Todaro Migration Model developed by reflecting on the Lewis Model [21,22]. The other is the theoretical model of urban and rural spatial polarization development represented by growth poles and a core periphery relationship [23]. Lipton believes that many countries divide urban and rural areas into two classes and implement "urban bias" policies, which lead to serious imbalances in urban and rural development [24,25]. The theory of unbalanced development between urban and rural areas dominated Western academic circles at that time.

After the 1980s, more scholars began to advocate urban–rural connection and coordinated development. Some geographers took the lead in challenging the trend of urban–rural division [26,27], and later, more international studies focused on coordinated development [28–30] and some new concepts were put forward. The pulling force of cities and the pushing force of rural areas in developing countries make cities and villages, and agricultural activities and non-agricultural activities, closely linked, and blur urban– rural boundaries [31]. The regional network development model holds that urban and rural areas generate stronger communication and networks through a series of "flows",

thus promoting the integration of urban and rural development [32]. In terms of politics, the economy, society and culture, the interaction and association of urban and rural form an "urban–rural continuum" [33–36]. Based on the five aspects of "food flow, resource flow, people flow, concept flow and capital flow", the interaction between urban and rural areas in developing countries is complex, and the "urban and rural dynamics" can reveal the complexity of urban and rural connection from the point of view of "livelihood strategy" and "resource allocation" [37]. Urbanization is transforming the planet, within and beyond cities, at all spatial scales [38]. The rural area (or countryside or the hinterland) has become key to the process of capitalist urbanization [39,40]. There are also many advanced practices in rural construction in Western countries, such as the "Bavaria experiment" in Germany, "New Village Movement" in South Korea and "city–village merger" in Japan. Taking the Bavaria experiment in Germany as an example, after World War II, the gap between urban and rural areas was further widened, and rural problems were prominent. Under the concept of urban–rural equivalence, district planning, land integration, agricultural mechanization, infrastructure construction, education development and other measures were started in rural areas, to make the rural and urban areas different in type but same in quality. The action is still popular in Germany for making the rural areas better [41].

With the evolution of the urban–rural relation theory, urban–rural governance has roughly gone through the process of the "co-governance of rural and urban, sub-governance of urban and rural, co-governance of urban and rural" [42]. After the industrialization of societies has begun, the gap between urban and rural development has increased, so different management methods have been adopted in urban and rural areas, that is, a separation of the administration of the urban and rural. Western countries have also experienced a process of change from urban–rural dual opposition to urban–rural integrated governance [43]. Since the 1990s, rural construction and governance have gradually become a research hotspot [44–50]. Such issues as rurality, the revitalization of the world's rural areas, the future of rural areas, the relationships between climate change and rural evolution, and food security have become the focuses of research [51–56]. The entrepreneurship of farmers, the development of rural finance and multicommunity cooperation are regarded as the keys to rural revitalization [12,57]. In different countries, governments, other organizations and volunteers play important roles [58–62]. The evolution of urban–rural relation theory reflects the trend of change from attaching extremely great importance to cities to attaching equal importance to both urban and rural areas.
