"So, through a chance turn of events, Obito took the gravely injured Shisui with him and placed a control mechanism on his heart, allowing him to use Shisui for his own ends. Shisui Uchiha was a genius among the Uchiha who had awakened the Mangekyō Sharingan back then. With Shisui's power, Obito successfully maintained considerable influence within the Akatsuki. Shisui's combat prowess was plain for all to see—he was even stronger than Obito himself. So, during the Akatsuki's operations, Obito began gaining more and more say through Shisui."
"Was there a serious power struggle within the Akatsuki before that?"
"No. Obito wanted more say mainly because of his own plans. The Akatsuki's founding had indeed been influenced by Obito's wishes while he was posing as Madara Uchiha, but that didn't mean their Leader, Pain, and the others supported his ideas unconditionally. Quite the opposite: after the death of Yahiko, the Akatsuki's previous Leader, Konan remained extremely wary of Obito."
"And as a 'minor' figure who followed Obito around, I felt that the logic their Leader, Pain, believed in actually conflicted with Obito's. Under those circumstances, Obito, who was already planning how to use the Akatsuki to further his own goals, discovered just how useful Shisui could be."
"The Akatsuki's nominal Leader was Pain, or Nagato. His idea was to recruit more people and expand the Akatsuki's strength. Once they had gained a measure of influence in all the Five Great Nations, they would begin collecting the tailed beasts and use the Demonic Statue of the Outer Path to concentrate their power into a single weapon. Then they would use that tailed beast weapon to threaten and control the Five Great Nations. His philosophy was to make every nation in the world experience the immense pain brought by war and power.