The main reason for the military reform carried out in the middle of the 16th century?

The main reason for the military reform of the mid-16th century is the failure of the previously existing squad in the conditions of modern wars. Ivan the Terrible created a semi-regular army called the Archers. This measure was aimed at the formation of regiments of a new system, since Russia suffered several defeats in the fight against the Crimean Tatars and the Livonian Order. The old army was untrained and weak. And the archers, formed from the noble layer, became the support of the monarch for many years. This situation consisted in the fact that in their free time the archers were engaged in economic affairs, and during the war they were mobilized.