In the face of the dual difficulties of economic globalization, unbalanced regional economic development and low resource allocation efficiency, the Belt and Road as an important platform for building a new development pattern in China and promoting international economic cooperation is playing an irreplaceable role. It is of great practical significance to accurately assess the impact of the Belt and Road initiative on the economic growth of domestic node cities. Taking the Vision and Actions for Jointly Building the Silk Road Economic Belt and the 21st Century Maritime Silk Road published in 2015 as a quasi-natural experiment, this paper constructs a two-way fixed-effect model and empirically tests the impact of the Belt and Road Initiative on the economic growth of node cities along the route and its mechanism by using a sample of 274 prefecture-level cities in China from 2009 to 2019. The results show that the “Belt and Road” initiative has a significant promoting effect on the economic growth of node cities along the route, which is still robust under the test of placebo test and PSM-DID model. And promoting the rationalization and upgrading of the industrial structure of node cities along the route is an important mechanism. Heterogeneity test shows that the promotion effect is more significant in less developed cities and inland cities.
On the one hand, in recent years, global economic growth has slowed down, geopolitical conflicts have occurred frequently, anti-globalization trends have risen, a new round of technological revolution is in full swing, and the global development pattern is facing great changes. On the other hand, when China achieves economic growth, the gap of regional development level remains high for a long time. Taking the data released by China’s National Bureau of Statistics in 2022 as an example, the GDP per capita of the 10 eastern provinces is 1.60 times that of the six central provinces, 1.77 times that of the 12 western provinces, and 2.03 times that of the three northeastern provinces. Based on a scientific judgment of the situation at home and abroad, in order to strengthen international cooperation, promote shared responsibility and win-win interests, deepen domestic reform and development in various fields, and push China’s vast inland regions and border regions to the forefront of opening up, the President Xi Jinping put forward the initiative of jointly building the Silk Road Economic Belt and the 21st Century Maritime Silk Road when visited Central Asia and Southeast Asia in September and October 2013. And on March 28, 2015, the National Development and Reform Commission, the Ministry of Foreign Affairs and the Ministry of Commerce jointly issued the Vision and Action on Jointly Building the Silk Road Economic Belt and the 21st Century Maritime Silk Road (hereinafter referred to as the Vision and Action), which made clear plans for the key provinces and cities of the Belt and Road Initiative.
By June 2023, China had signed more than 200 cooperation documents on Belt and Road cooperation with 152 countries and 32 international organizations, and made a series of achievements in railway and shipping infrastructure construction, import and export quarantine and customs cooperation, industrial chain cooperation, multilateral investment and financing cooperation, cultural exchanges, and entry-exit tourism cooperation. The total trade volume between China and countries along the Belt and Road increased from 1.63 trillion dollars in 2013 to 2.9 trillion dollars in 2022, and the cumulative trade volume exceeded 19.1 trillion dollars. From 2013 to 2022, China’s direct investment in countries along the Belt and Road exceeded 240 billion US dollars, and those countries’ direct investment in China exceeded 140 billion US dollars. Therefore, it is of great significance to empirically evaluate the impact and mechanism of the Belt and Road Initiative on the economic development of key provinces and cities along the route.
Existing studies on the economic effects of the Belt and Road initiative are mainly theoretical studies, while empirical studies mostly focus on national level such as location choice, trade potential, and scientific and technological innovation, while there are few relevant studies on the empirical test of its impact on domestic node cities along the route and its mechanism. Moreover, compared with China’s traditional major trading partners, many countries along the Belt and Road have a lower level of development, a lower level of openness, and backward service and manufacturing industries. What impact will the development of economic and trade relations between China and countries along the Belt and Road have on China’s regional economic growth is an important issue related to the correct handling of the relationship between openness and coordination in our country. It is of theoretical value and policy significance to study the influence of the Belt and Road Initiative on China’s regional economic growth. Therefore, this paper takes the release of the Vision and Action of the Belt and Road as a quasi-natural experiment, takes the data of 274 prefecture-level cities from 2009 to 2019 as samples, and uses the difference-difference model and fixed-effect model to test the impact of the Belt and Road initiative on the economic development of node cities and its main mechanism. The results demonstrate a significant promoting effect of the Belt and Road initiative on the economic growth of node cities along the line, and promoting the rationalization and upgrading of the industrial structure of node cities is an important mechanism. Heterogeneity test shows that the promoting effect is more pronounced in less developed cities and inland cities.
Compared with the existing literature, the possible marginal contribution of this paper is mainly reflected in the following aspects:
First of all, existing studies mainly discuss the impact of the Belt and Road Initiative on country’s economic growth and trade competitiveness. This paper shifts the perspective from external to internal, and uses prefecture-level city data to focus on city economic growth, which is a useful supplement to related fields.
Secondly, in the research design, the robustness test was carried out using PSM-DID (propensity score matching difference-difference model) model, which overcame the systemic bias and endogeneity problems of the model to a certain extent, and effectively identified the causality.
Finally, this study explores the mediation effect of industrial structure upgrading and the heterogeneity of regional and economic development level, which enriched the evaluation conclusions of the policy effect of the Belt and Road initiative.
The remainder of this paper is organized as follows. Section 2 contains a review of the related literature. Section 3 displays empirical model setting and data description. Following that is empirical result analysis and further discussion on the mechanism. The last section concludes this paper.
In general, the Belt and Road is a new channel and network of economic and trade between China and neighboring countries in Central Asia, Eastern Europe and Southeast Asia, which is of great significance for the economic opening up of China’s inland regions, the transformation and upgrading of the industrial structure in the eastern region (Dong & Lin, 2015) . After the implementation of the Belt and Road Initiative, the role of gateways in central and western China in foreign trade has gradually increased (Li & Jiang, 2020) .
In terms of trade and investment, with the continuous development of the Belt and Road construction, the density of trade and investment networks among countries along the route is increasing. The Belt and Road Initiative has significantly promoted the growth of China’s trade with countries along the route (Sun et al., 2017) , but trade complementarity is still greater than competition, which is an important condition for the gradual increase of China’s exports to countries along the route (Li et al., 2017) . Moreover, the hard-working and brave entrepreneurship of China’s foreign economic and trade practitioners, as well as the foreign policy of “peaceful coexistence and non-interference in each other’s internal affairs” that China has always adhered to, also become new comparative advantages in bilateral trade with countries along the Belt and Road (Li & Yan, 2018) , which further promotes trade between China and countries along the Belt and Road. The Belt and Road Initiative has also promoted China’s direct investment in the countries along the route. After the implementation of the Belt and Road Initiative, the number of investment projects of Chinese enterprises in the countries along the Road has increased by 15.9% - 31.3% (Lv et al., 2019) .
In terms of industrial structure, China’s direct investment in countries along the Belt and Road can separate industries or production links that have lost their comparative advantages, thereby improving China’s position in the global value chain (Peng & Li, 2018) . With the global flow of production factors and the gradual evolution of the international trade pattern, the trade of intermediate products has become the main form for countries to participate in the international division of labor. China can comply with the law of comparative advantage and transfer some excess industries and overcapacity to countries with lower economic development level to adjust its own industrial structure (Huang & Yu, 2017) . And countries along the Belt and Road have the conditions to undertake China’s industrial transfer, and can upgrade their domestic industrial structure with the help of international industrial transfer (Zhang et al., 2016) . By studying the international division of labor, industrial correlation and complementarity between China and countries along the Belt and Road, it can also be found that China has the ability to dominate the regional value chain of the Belt and Road (Wang & Wu, 2018) . Participation in the construction of the Belt and Road can upgrade the value chain status and the efficiency of the international division of labor of China and countries along the Road.
There are many factors affecting economic growth. Existing literatures have discussed the factors affecting regional economic growth from the aspects of labor, capital, technology and other production factors levels, industrial upgrading, value chain division and other industrial levels, government competition, tax policies, marketization degree and other institutional levels.
In terms of production factors, Cai et al. (2001) believe that the lag of labor market development leads to the distortion in resource allocation, and the flow of population plays a decisive role in expanding or delaying the regional economic growth gap (Duan & Liu, 2005) . Through the analysis of FDI panel data, Wan (2006) believes that regional differences in domestic investment are the main cause of regional economic differences, and foreign direct investment is also one of the important reasons for aggravating China’s dual economic structure. In the process of social and economic development, the connotation of production factors has been enriched, science, technology, management and information have entered the production process and playing an increasingly important role in regional economic growth (Wu et al., 2011) .
At the industrial level, the upgrading of industrial structure is essentially the importance of various industries changes according to an evolution law (Rostow, 1959) , which was initially dominated by agriculture, then replaced by manufacturing industry, and finally replaced by the tertiary industry. This upgrading process is also a process of optimizing the allocation of production factors, which gradually flows from low-efficiency industries to high-efficiency industries, thereby improving social productivity and driving economic growth (Peneder, 2003) . China is going through this process. At present, China’s tertiary industry is developing rapidly, providing continuous momentum for economic development, especially the producer service industry is becoming a new driving force for economic development (Li et al., 2017) .
In addition, the degree of regional openness to the outside world (Zhao, 2001) and regional protection policies (Young, 2000) are also important factors affecting regional economic growth. For example, the Chinese government’s special incentives in foreign exchange retention, fiscal handover, taxation, financial credit and investment project approval have greatly promoted the rapid economic development of the eastern coastal areas (Deng, 2005) .
The Belt and Road initiative can promote the transfer of excess and backward production capacity to countries along the route, promote technological exchanges and cooperation between China and countries along the route, promote the cooperation between China and countries along the route in the tertiary industry such as cultural tourism, and then upgrade China’s industrial structure, and the upgrading of industrial structure can affect economic growth through factors allocation, technological progress and other mechanisms. Based on the above analysis, this paper proposes the following research hypotheses.
H1: The Belt and Road Initiative can promote the economic growth of node cities along the route, and an important mechanism is to promote the upgrading of the industrial structure of node cities along the route.
Under the law of diminishing marginal effect, the initiative may have a heterogeneous effect on cities with different economic bases. Before the initiative was put forward, developed areas are earlier than less developed areas in the upgrading of industrial structure. Therefore, it can be inferred that the initiative has a greater role in promoting the economic growth of less developed cities and a smaller role in promoting the economic growth of developed cities (Wang & Tian, 2021) . At present, the developed cities are mostly located in the coastal areas, while the less developed cities are concentrated in the inland areas.
H2: According to the law of diminishing marginal effect, compared with coastal and developed cities, the Belt and Road Initiative has a more pronounced role in promoting the economic growth of inland and less developed cities.
With reference to most of the existing researches on the economic effects of the Belt and Road initiative, this paper takes the Belt and Road Initiative as a quasi-natural experiment and adopts the Difference-in-Difference (DID) model to examine the effect of the Belt and Road Initiative on the economic development of node cities. On March 28, 2015, the National Development and Reform Commission, the Ministry of Foreign Affairs and the Ministry of Commerce jointly issued the Vision and Actions to Promote the Joint Construction of the Silk Road Economic Belt and the 21st Century Maritime Silk Road, which mentioned a total of 26 important node cities along the Belt and Road : Xi’an, Xining, Shanghai, Tianjin, Ningbo, Lanzhou, Zhoushan, Guangzhou, Shenzhen, Hefei, Nanchang, Changsha, Wuhan, Zhengzhou, Chongqing, Chengdu, Sanya, Zhanjiang, Shantou, Qingdao, Yantai, Dalian, Haikou, Fuzhou, Xiamen, Quanzhou. In view of the serious lack of data during the sample period of Nanchang City, it is not discussed in the analysis. Referring to the study of Liu (2022) , in this study, the above 25 node cities were used as the treatment group, and the other cities were used as the control group. The baseline regression model is as follows:
Lngdp i t = β 0 + β 1 Treat i × Post t + γ X i t + θ i + μ t + ε i t (1)
where the subscript t and i represent the sample cities and time periods respectively, the explained variable Lngdp is the economic development level of the prefecture-level city, the specific index is the logarithm of the total GDP of the prefecture-level city, and the interaction term Treat × Post is the net policy effect of the Belt and Road initiative. The estimator of the coefficient β 1 reveal the impact of the Belt and Road Initiative on the economic development of node cities. X represents a series of control variables, θ and μ are fixed effect at the city and year levels, respectively. ε represents the random disturbance term.
a) Explained variable: the economic development level. Referring to Lv et al. (2019) , this paper uses the logarithm of node city GDP to represent the economic development level of the node city.
b) Key explanatory variable: the Belt and Road initiative. The impact of the initiative on the economic development of note cities along the route is measured by which represents the interaction term between the dummy variable of implementing the initiative and the dummy variable of time. Treat = 1 represents the 25 Belt and Road node cities mentioned above, treat = 0 represents non-Belt and Road node cities; Since 2015 was the first year to officially transform the Belt and Road construction from concept to action, this paper sets 2015 as the implementation time of the initiative, dummy variable takes the value of 0 before 2015 and 1 in 2015 and onwards.
c) Control variables: Considering that there are many factors that can promote economic development, if these factors are not well controlled, they will interfere with the empirical results. In order to obtain accurate experimental results, refer to the studies of Liu and Zhao (2015) and Wu and Han (2022) , six variables including fixed investment level (Fix), foreign direct investment level (Fdi), education level (Edu), government scale (Gov), science and technology expenditure ratio (Tec) and employment level (Emp) were added to the empirical model as a series of control variables affecting economic development. The specific meanings and descriptive statistics of all variables are shown in