This chapter explores the harmonization and diversification of conflict-of-law rules in international contract disputes, comparing approaches in Japan, South Korea, China, the European Union (EU), and the United States. While many jurisdictions have modernized their legal frameworks to align with global trends, the United States remains an exception due to its decentralized legal structure. The harmonization of conflict-of-law rules enhances legal certainty and economic integration while preserving national interests. Japan, South Korea, China, and the EU have moved toward unification, demonstrating the benefits of a structured and predictable legal framework. This paper underscores the importance of legal scholarship, comparative law, and economic interdependence in shaping private international law, advocating for continued efforts toward legal harmonization to promote stability in global commerce. By exploring alternative approaches to harmonizing conflict-of-law rules through autonomous legislation and comparative law, this chapter highlights the complexities and nuances of international contract disputes. The findings suggest that harmonizing conflict-of-law rules is crucial for legislators to serve the interests of global users, ensuring stability and predictability in an increasingly interconnected world. Ultimately, this chapter contributes to the ongoing discourse on private international law, offering insights and recommendations for future legal developments.