Strapped for resources and confronting multiple internal and external challenges, the Ottoman empire could not hope to mount against its Russian rival either a comparable military threat or an effort at subversion. Its armed forces could pose no credible threat, and for subversion it lacked the resources and funds to foment turmoil inside Russia and challenge the Russian state's authority. Nor did it possess the international clout that might have permitted it to exploit Russia's own internal fractures in diplomatic arenas. Nonetheless, the Ottomans were not wholly incapable of projecting influence into the Russian empire. The Russian empire had some fifteen to twenty million Muslim subjects; more, in fact, than lived under the sultan. But the Ottoman empire was the world's greatest independent Muslim state, and as such it could not but perform as a symbol and barometer of the well-being of Islam for Muslims around the world. In addition, the Ottoman sultan had a claim to be the caliph, the successor to the Prophet Muhammad as the head of the community of Sunni Muslims, i.e., the great bulk of Muslims in the world and in Russia outside Azerbaijan. Sultan Selim I first claimed the mantle of caliph for the Ottomans in 1516 when he came upon a descendant of the last Abbasid caliph living among the Mameluks whom he had just defeated.