Because of the Gempei
War (1180-1185) Japan had two rulers. One being the god-like emporer
the other being the Shogun in whose hands the emporer was but a puppet.
However, around 1550 the bloody civil war caused the office of shogun
to be just as powerless as the emporer.
The real power was held by the different Daimyo who were firstly warriors and secondly administrators. They lived a life of constant war.
For example : Two Warlords, Takeda Shingen and Uesugi spent over a decade fighting over the same place year after year. Between these two massive Titans were a bunch of smaller families also involved in trying to steal each others lands.