The global footprint of East Asian diasporas—particularly those originating from China, Japan, and Korea—has expanded markedly over the past century. Their presence across Southeast Asia, North America, Europe, and other regions has produced a complex web of cultural, economic, and political influence, while simultaneously raising nuanced security considerations for both home and host countries. This chapter investigates the dual narrative of diaspora contributions and their perceived or actual entanglements with national and regional security dynamics. Grounded in an interdisciplinary approach that draws on migration theory, securitization theory, and political economy, it explores how East Asian diasporic communities shape host societies through remittances, business investment, cultural diplomacy, and transnational soft power. At the same time, it examines how these communities are often situated within geopolitical anxieties, surveillance regimes, and identity-based scrutiny. Through case studies including Chinese diasporas in Southeast Asia, Zainichi Koreans in Japan, and Korean-American political mobilization, the chapter explores how diasporas simultaneously act as agents of connection and objects of state concern.