Historically, arms races generate a great deal of interest both in the academia and policy circles for a variety of reasons. They are widely believed to have significant consequences for states' security. In the debate over their consequences, one side holds that arms races increase the probability of war by undermining military stability and straining political relations. The opposing view holds that engaging in an arms race is often a state's best option for avoiding war when faced with an aggressive adversary. The 21st Century is witnessing the return of arms race amongst states. Coupling with the advancements in technology, the menace of arms race in the 21st Century, therefore, if not curtailed could lead to war more devastating than witnessed in the last century. Using basic content analysis the study revealed that the 21st Century arms races are mainly in the area of nuclear weapons, hypersonic missiles, missile defence, cyber-warfare, and space weaponisation. The arms races are prominently amongst the world‟s great powers such as the United States of America, Russia, and China as well as developing states like Iran and North Korea. This study discovered that nuclear weapons are still at the forefront of arms race in the 21st Century, despite efforts to reduce their role in global affairs and to negotiate further reductions in quantity. Also, states like the USA, China, and Russia are exploiting the advantage of speed and manoeuvrability to engage in arms race in hypersonic missiles. This has prompted nations to compete in the development of missile defences in order to counter the present missile threats. Furthermore, in anticipation for future warfare, nations such as the USA, China, and Russia are in arms race to weapon sise space by deploying space to space, earth to space and space to earth weapons, where appropriate. War in the 21st Century could in turn lead to more human, material, and environmental casualties due to the latest advancement in technologies and modernisation of existing weapons and associated equipments. Consequently, measures are needed to ensure that arms races in the 21st Century, if not eliminated, are reduced to the barest minimum in order to promote international peace and security. Renewed commitments on existing arms control measures, formulation of new arms control measures, and the complete elimination of nuclear weapons are the measures that could be considered.