In most countries, the armed forces are divided into three or four forces: an army, a navy, an air force, and often a gendarmerie or a paramilitary police force. Many countries have a variation on the standard model of three or four basic forces. Variations include China (army, navy, air force, strategic missile force), Japan (Ground Self-Defense Force, Maritime Self-Defense Force, Air Self-Defense Force), and North Korea (Ground Forces, Navy, Air Force; civil security forces). The United States has five (army, navy, air force, marines, coast guard).

Armed forces may be organized as standing forces (e.g. regular army), which describes a professional army that is engaged in no other profession than preparing for and engaging in warfare. Korea has compulsory military service; conscript service obligation is 24-28 months, depending on the military branch involved (to be reduced to 18 months beginning 2016).

This list of six countries by size of armed forces displays national troop levels by active troop strength. This list is indicative only, as strict comparisons cannot accurately be made. For example, “troop strength” in some forces might include administrative or paramilitary functions that in another country might be civilian roles and therefore excluded from the below figures.

This chart of six countries by size of military capabilities displays tank, destroyer, frigate, corvette, nuclear submarine, conventional submarine, fighter aircraft and nuclear weapons.