The primary reason of Wagner rising up given by Prigozhin himself: 1. The senior brasses of armied forces has deliberately delayed or shorted or even not provided the supplies of Wagner in the battlefield and this leaded to many Wagner fighters death and mission failure; 2. The regular army has attacked Wagner troops under the order of those senior brasses, even though Defence of Russia has denied it, as well as Defence of Russia attempted to take control of Wagner from Prigozhin himself; 3. Russia and the president was deceived by the senior brasses who just care about their interest rather than the interest of Russia, so actually there is no proper excuse to launch the so-called 'special military operation' against Ukraine.
