军事（Military），即军队事务，古称军务，是与一个国家及政权的国防或武装力量相关的学问及事务。

军事在上古时代时已经出现，虽然并无实据，但根据传说，九黎部落首领蚩尤有81名兄弟，都是铜头铁额。他们还懂得制造金属兵器，在器具水平落后的远古时期，这是很重要的军事优势。后来蚩尤的部落与黄帝和炎帝的部落爆发了涿鹿之战，双方展开了长久的战争，黄帝和炎帝最后胜利，把他擒杀。

战国时期，秦国秦孝公奋发图强，任用商鞅，实行了两次变法，使秦**力增强，为后人秦始皇的一统天下打下了基础。最后由始皇统一中国，创建秦朝。

The military, also called the armed forces, are forces authorized to use deadly force, and weapons, to support the interests of the state and some or all of its citizens. The task of the military is usually defined as defense of the state and its citizens, and the prosecution of war against another state. The military may also have additional sanctioned and non-sanctioned functions within a society, including, the promotion of a political agenda, protecting corporate economic interests, internal population control, construction, emergency services, social ceremonies, and guarding important areas. The military can also function as a discrete subculture within a larger civil society, through the development of separate infrastructures, which may include housing, schools, utilities, food production and banking.