THE WAR ON THE RUSSIAN BORDER.--Along the Russian frontier also the Allied cause met with serious reverses. The year had opened favorably with the Russians in control of most of Galicia. In March the great Galician fortress of Przemysl, which had successfully withstood the attacks of the Russians the previous autumn, was compelled to surrender. Meanwhile, in January, Russia once more attempted to carry out the other part of her general plan, the invasion of East Prussia. The Russian troops succeeded as before in entering the coveted territory, this time crossing the troublesome lake region while the waters were frozen. Soon, however, the invaders met with a decisive defeat. In the Battle of the Mazurian Lakes, General Von Hindenburg took 100,000 Russian prisoners; the number of killed and wounded Russian soldiers is said to have been 150,000. The Russians hurriedly retreated from German soil. The time had now come for the Germans and Austrians definitely to assume the offensive. A strategic blow in Galicia imperiled the whole Russian front and compelled a general retreat of the Russian armies in Galicia and Poland. In June both Przemysl and Lemberg were recaptured by the Central Powers. By September all of Russian Poland had been conquered. Russia had lost 65,000 square miles of thickly populated territory. But the land was so thoroughly plundered by the German conquerors that many of the people died of starvation. BULGARIA ENTERS THE WAR.--The sympathies of the Bulgarian government had been with the Central Powers from the beginning of the war. Bulgaria had not forgiven the neighboring Balkan states for their treatment of her in the second Balkan war (1913). Against Serbia her feeling was particularly bitter. The Allied disaster at Gallipoli and the military successes of Germany and Austria in Poland and Galicia in the spring and summer of 1915 led the Bulgarians to believe that now was the time for them to strike. In October Bulgaria declared war upon Serbia, thus definitely taking her stand as an ally of the Central Powers. Bulgaria's entrance into the war was followed by simultaneous invasions of Serbia from Austria and from Bulgaria. Under these blows the Serbians were crushed. Together with her neighbor and ally, brave little Montenegro, Serbia was overrun by her enemies. The cruelties inflicted upon the Serbian population by the invading Bulgars are said to have been fully as horrible as those which had taken place during the conquest of Belgium in 1914 and of Poland in 1915.