An Army is the name given to the hierarchical military organization established within a social group. The main function of an army is to safeguard the living conditions of this active society. It is a group of people who use their functions to provide security and protection to the city. The history of the armies comes from when man stepped on the ground, because when nomads, they formed groups and remained united as much as possible, to guarantee the safety of all against the environment that surrounded them, at that time, unknown. Always the principles of defense of a nation are valued from the military point of view, in order to maintain order and discipline, which are better inspired by amilitary institution.

The main component of an army are soldiers, they are people trained in various aspects in which discipline and defense are relevant, to provide the corresponding service to the nation. On some occasions in history, civil armies have been observed, defending particular causes, usually against a dictatorial regime that also has an official and armed army. The military armies are to provide defense service to the nation, however, before a more dangerous situation arises, the police It will provide a useful reconnaissance service, when the execution of a larger security plan is warranted, the concept of military army will be applied.

There are countries where men, upon reaching an average age, must comply with what is called military service, that is, they must be part of the country's military army, an example of these countries is Hong Kong, if they do not comply with this process men should be punished with jail. There are also countries that do not have an army, they limit themselves to having a police force and an honor guard that protects government or religious entities. The armies can be of the sea, air, amphibian or land, it all depends on the battlefield and the transport methods they use. These divisions contribute to the state that possesses them having a complete defense system that covers all possible attack flanks .