The infantry of the Janissaries, one of the Ottoman Empire's foremost institutions in the 19th century, had now fallen into decline and corruption. It developed into a corps of civil servants who did perform the job assigned to them, resulting in the Empire paying for a non-existent army and forced to hire mercenaries. As part of his plan of reforms and, also, taking advantage of the events of the Greek Revolution, Sultan Mahmoud II also made changes to the army, trying to modernize it and bringing in Europeans for its training. But these changes triggered the rebellion of the Janissaries, who had been fighting for years hard against Mahmoud. The Sultan took the opportunity to rid himself of them, crushing the rebellion and exterminating the rebels (early June), resulting in the purge of the internal political ground. The massacre of the Janissaries became known as the "Happy Event"