Although the recent Turkish concessions to Russia left to the Czar no ground for war, a pretext was supplied by Sultan Mahmoud himself. With true Turkish infatuation he chose this moment to issue a direct challenge to Russia. The Czar was denounced as the instigator of the Greek rebellion, and the arch enemy of Islam. The treaty of Akerman was declared null and void. A holy war was proclaimed against the Muscovites. "The Turk does not count his enemies. If all the unbelievers together unite against us we will enter on the war as a sacred duty, and trust to Allah for help." This proclamation was followed by the expulsion of all Christians from Constantinople. Unfortunately for the Sultan, his recent massacre of the Janizaries deprived him of the flower of his troops, and the reorganization of the Turkish army, which was the motive of that act, was only under way. For seven years the Russians had been preparing for this war. Nicholas lost no time in answering the Sultan's challenge. He replied with a declaration of war on April 26. Field Marshal Wittgenstein crossed the Pruth, while Paskievitch entered Asia Minor. The Russian troops overran the Roumanian provinces, Wallachia and Moldavia. The Danube was crossed early in June, under the eyes of the Czar. Unable to meet their enemy in the open field, the Turks withdrew into their strongholds, Ibraila and Silistria on the Danube, Varna and Shumla in the Balkans. The Russians besieged and stormed Ibraila, and thence pushed on through the Dubrudsha toward the Black Sea. In the meanwhile Paskievitch in Asia Minor defeated two Turkish armies and captured Erzeroum. [Sidenote: Brionis victorious] [Sidenote: Surrender of Varna]