The sengoku period came about after the end of the Onin War and left a power vacuum as to who was the ruler of Japan and started the power struggle between local daimyos who fought each other for power, glory, land and control over the shogun and his broken lands. The Sengoku period involved major changes on the battlefield with castles being built with a stone base rather than wood, the introduction of muskets through trade with the Europeans, siege work and new tactics involving many squadrons of well-organized warriors rather than the honorable 1 on 1 fights between samurai on the battlefield.
When looking into the Sengoku period there are two processes which should be looked into the first being fission and the second being fusion. Fission is what occurred at the time of the collapse of the shogun which gave daimyo a chance and reason to battle each other for various reasons. A prime example of the process of fission is the hojo family who used the lawlessness of the sengoku period to build up their family from a band of 6 men to an army of tens of thousands. Hojo Soun was an unknown samurai whose sister married into an illustrious family (imagawa yoshitada) when he was killed in battle in 1480 his sons inheritance was placed in great peril, due to this Soun came to his assistance with the original 6 men and settled the matter. The grateful heir rewarded him with a castle this was merely the first acquisition of many for the Hojo family. Soun added the Izu province to his territories after provided further help in another matter, by 1518 soun add further added to his territories one being the family’s future capital (odawara) though