Playbook: Start War with anyone.
Let's assume there's a country named MatrixLand and its neighbor is NOTMatrixLand.
MatrixLand creates an organization named KillerZ, which operates undercover in NOTMatrixLand.
MatrixLand can instruct KillerZ to attack MatrixLand and kill some of its residents.
Then, MatrixLand can say, "Look, world! KillerZ attacked us. We have no choice but to go to NOTMatrixLand and eliminate everyone to find KillerZ. By the way, anyone could be part of KillerZ."
Allies of MatrixLand are now required to ban the NOTMatrixLand flag, claiming it symbolizes support for KillerZ.