This dissertation centers on the theme of regioanl disparities, employing a varitety of models and methodologies to explore the impacts of different policies on various  regions. Specifically, it investigates three main issues: the effect of China's High-Speed Rail network on regional economic disparities, the impact of the EU's enlargement in 2004 on the production segmentation within EU NUTS2 regions and the infuence of the EU-South Korea FTA on production fragmentation across various EU regions and industries. Together, these studies weave a complex narrative on the interactions between trade policies, infrastructure development, and regional economic dynamics, offering a comprehensive understanding of how macroeconomic policies and investments shape the economic and social landscapes of regions within large economies.