What caused japanese disunity from the 1300s to the 1500s?

From 1300s to 1500s, which is about two centuries, Japan tore itself apart in the feudal wars and all the civil conflicts. Due to Minamoto's victory, Japan transitioned to medieval feudalism and power rested upon two shogun regimes, the Kamakur and Ashikaga. 

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.

the answer is d. amendments.