Another reason for the Russian advance in Galicia was her desire to control the Galician oil wells. To Germany petrol had become one of the foremost munitions of war. Since she could not obtain it from either America or Russia she must get it from Austria, and the Austrian oil fields were all in Galicia. This, in itself, would explain the Galician campaign. Moreover, through the Carpathian Mountains it was possible to make frequent raids into Hungary, and Russia understood well the feeling of Hungary toward her German allies. She hoped that when Hungary perceived her regiments sacrificed and her plains overrun by Russian troops, she would regret that she had allowed herself to be sacrificed to Prussian ambition. The Russians, therefore, suddenly, moved toward Cracow. Then von Hindenburg came to the rescue. The supreme command of the Austrian forces was given to him. The defenses of Cracow were strengthened under the direction of the Germans, and a German army advanced from the Posen frontier toward the northern bank of the Vistula. The advance threatened the Russian right, and, accordingly, within ten days' march of Cracow, the Russians stopped. The German offensive in Poland had begun. The news of the German advance came about the fifth of October. Von Hindenburg, who had been fighting in East Prussia, had at last perceived that nothing could be gained there. The vulnerable part of Russia was the city of Warsaw. This was the capital of Poland, with a population of about three-quarters of a million. If he could take Warsaw, he would not only have pleasant quarters for the winter but Russia would be so badly injured that no further offensive from her need be anticipated for a long period. Von Hindenburg had with him a large army. In his center he probably had three-quarters of a million men, and on his right the Austrian army in Cracow, which must have reached a million. Counting the troops operating in East Prussia and along the Carpathians, and the garrison of Przemysl, the Teuton army must have had two and a half million soldiers. Russia, on the other hand, though her mobilization was still continuing, at this time could not have had as many as two million men in the whole nine hundred miles of her battle front. The fight for Warsaw began Friday, October 16th, and continued for three days, von Hindenburg being personally in command. On Monday the Germans found themselves in trouble. A Russian attack on their left wing had come with crushing force. Von Hindenburg found his left wing thrown back, and the whole German movement thrown into disorder. Meanwhile an attempt to cross the Vistula at Josefov had also been a failure. The Russians allowed the Germans to pass with slight resistance, waited until they arrived at the village Kazimirjev, a district of low hills and swampy flats, and then suddenly overwhelmed them.