Complex sentence: After Motouji, all the "kubō" wanted power over the whole country, and the "Kantō kubō" era is therefore essentially a struggle for the shogunate between the Kamakura and the Kyoto branches of the Ashikaga clan.
Split into simpler sentences: After Motouji, all the "kubō" wanted power over the whole country. The "Kantō kubō" era is therefore essentially a struggle for the shogunate between the Kamakura and the Kyoto branches of the Ashikaga clan.