戰爭是人類歷史上不斷發生的現象，整個人類歷史幾乎就是一部戰爭與和平交替存在的紀錄。戰爭的發生也總是帶給受波及的人無限的痛苦，及影響著戰後的政經發展，因此，對戰爭的研究實屬必要。本文擬從現實主義的角度，探討戰爭的起因以及預防之道。現實主義認為國際政治乃屬於無政府狀態，而國家都是自利的行為體，為了自保而發生衝突乃不可避免的結果。在無政府狀態下，為了防止戰爭的發生，國家間只有藉助權力平衡的手段，才能遏止他國的侵略野心，戰爭的發生往往是權力失衡的結果。但現實主義的另一支派，霸權穩定論者則辯稱，霸權國的存在，而非權力平衡，才是維持國際和平的保障。不論是權力平衡或是霸權穩定論，現實主義過分強調權力的追逐及運用，往往導致權力的過度擴張而釀成衡突或侵略行徑。因此，搭配自由主義以及建構主義的做法，才能彌補現實主義的缺憾，以防止戰爭的發生。

　　　　　"War" is a recurrent event throughout history, and the human history is a record of alternations between war and peace. The occurrence of war always brings abysmal pains to its victims and makes impact on the post-war political and economic development; therefore, the study of war is necessary. In this paper, we try to look at the causes of war and its preventions from the realistic perspective. It is the belief of realism that inter-state politics is anarchic, as all the sates are actors driven by self-interest, for whom conflict is an inevitable means to self-protection. In anarchy, states can only resort to balance of power to stop the invasive ambitions of other states in order to prevent the occurrence of war, which is usually the results of the imbalance of power. But another sect of realists, the theorists of hegemonic stability, argues that the assurance of inter-state peace relies o the existence of hegemonic states rather than the balance of power. No matter for the balance of power or the hegemonic stability, realism overly stresses the pursuit and manipulation of power, which usually leads to the undue extension and of power and results in conflicts and invasions. Therefore, to prevent war from happening, realism has to be employed along with liberalism and constructivism.