China’s Partnership Diplomacy as a Political Influence Strategy: Evidence from Sino-Vietnam Relations and a Multi-Country Difference-in-Differences Analysis

Abstract China has made partnership diplomacy the central organizing framework of its foreign relations, yet little is known about whether upgrading partnership ties produces measurable political effects. This study conceptualizes partnership upgrades as an institutional mechanism through which China signals commitment, embeds expectations, and deepens political–economic engagement with partner states. We adopt a mixed-method design that integrates a process-tracing analysis of China–Vietnam relations with a multi-period difference-in-differences (DID) model covering 200 countries from 1997 to 2022.The empirical results show that partnership upgrades significantly increase bilateral trade flows and high-level political exchanges. The magnitude of these effects varies across geopolitical and economic contexts: upgrades generate stronger political–economic linkages with Asian neighboring states and with “node-pivot” countries of strategic value, while OECD partners exhibit asymmetric patterns—strong economic responses but limited political alignment. Mechanism tests further reveal three dynamics: (1) economic cooperation displays a cumulative time-lag effect; (2) higher-tier partnerships have symbolic importance but do not automatically translate into proportionally stronger interaction; and (3) China-led bilateral and multilateral cooperation platforms amplify the political–economic impacts of upgrades.These findings indicate that partnership diplomacy functions as an institutionalized strategy of political influence in China’s foreign policy, shaping patterns of interdependence and structuring China’s engagement with diverse partner states. JEL Classification: F59 F19 O53