This paper critically examines the dual role of military alliances in contemporary international relations, particularly focusing on their impact on global stability and regional cooperation. By analyzing historical and modern examples, including NATO and the interactions among the United States, China, and Russia, the study elucidates how military alliances have transitioned from Cold War security mechanisms to multifaceted entities confronting today's geopolitical complexities. It delves into the security dilemmas alliances face, their strategic contractions, and the unique challenges posed by China's ascendancy and the ongoing Russia-Ukraine conflict. The paper underscores that while these alliances are pivotal in upholding global order, they also generate substantial obstacles to regional cooperation, especially in East Asia. This dichotomy is evident in the alliances' evolution, which reflects a shift from primarily defensive postures to roles that encompass economic and diplomatic dimensions, influencing regional dynamics and power balances. This paper demonstrates the various differences and contradictions between today's military alliances and regional cooperation, including contradictions in mechanisms, differences in concepts, overlaps in functions, and conflicts of practical interests. The findings advocate for a reassessment of military alliances, suggesting that future frameworks should foster trust and inclusivity, accommodating the diverse interests of regional actors to enhance cooperative security and stability.