I think the real question is, Why didn't Fugaku Uchiha ( Sasuke and Itachis' father) pursue more diplomatic ways for him to rule the village, rather then plan a coup da tet .
Also who or what influenced Fugaku Uchiha to plan a coup da tet in the first place ?
My opinion is Madara got to fugaku, told him Uchiha Senju History. (him being the captain of Konoha military police in essence made him in charge of Uchiha clan, best person to manipulate. )
ideas and thoughts ?
Edit, Madara failed with Kyuubi, so next best option that was available was to have Uchiha & Konoha take each other out in a civil war. ( like Madara said to sasuke a civil war would of been a great opportunity for rival villages to attack )
when Itachi found out about Madara, he proposed leave Leaf alone and in return you get revenge on Uchiha, etc Itachi helps out Madara etc.