The army of England before the Norman Conquest consisted of the king's household troops (housecarls) and all freemen able to bear arms, who served under the fyrd system for two months a year.

The fyrd was the Anglo Saxon militia, usually raised from freemen in a village or shire. It was used mainly to protect the locality except in times of war where they would be expected to fight anywhere in the country. The fyrd was organized to great effect by Alfred the Great. To avoid the problem of desertion he rotated the fyrd. 2 months on and 2 months off. This way he could be assured of their loyalty because their land would be tended by their kin who were at home.

After their invasion in 1066, the Normans introduced the feudal system, which existed in England until 1351, with changes in society resulting from the Black Death (labour shortage, population became more mobile between country and cities hence weakened links with their feudal lords.

In the feudal system, the monarch owned all the land but allowed favored individuals the use of it, as tenants, in exchange for service. The tenancies were called "feuds", "fees", or "fiefs", and the tenants would further pass on rights down to others in their retinue. King to overlords, overlords to vassals, vassals to serfs.

The service one rendered in exchange for land 'ownership' could be anything from military service to the King, or it could be a 'sergeantry' such as delivering grain.   The key points of the feudal system were that ultimately the King retained control, and that payment of some kind was made. True personal land ownership was impossible because the title one held was always subservient to the King.

Mercenaries were employed during the Hundred Years' War (1337-1453) and the Wars of the Roses (1455-85) in combination with the militia. With the Battle of Crécy in 1346, archers became important, the longbow being a major innovation of warfare. Also that day, Knights (the first shock troops) were countered and lost their place of dominance on the battlefield.

In post-feudal times, - when an army (typically an expeditionary force) was needed, the monarch would summon parliament to (hopefully) grant monies expressly for that purpose. The taxes levied as a result were the equivalent of the feudal service.