Meanwhile there was some excuse for the German choice. There was safety enough for the moment in France and Flanders, and events justified Germany's confidence that no Entente attack in 1915 could seriously disturb the German lines. No such grounds for complacence existed on her Eastern frontiers. East Prussia was not yet free, and graver danger threatened the Hungarian ally on which the Prussian relied only less than he did on himself. Galicia was in Russian hands, and Russian man-power was thought to be inexhaustible. The menace on both the Carpathian and the Prussian flanks could only be properly met by destroying the central position in Poland, and persistence in the attacks on Warsaw was essential to German strategy in the East. The frontal attack at the end of January which failed for the third time was followed by a flanking attack on the Niemen which also failed, and then by a drive on the southern flank in Galicia which turned the whole Russian front of 900 miles, led to a wholesale retreat, and precipitated the greatest set-back the Allies suffered in the war. Germany failed against the democracies of the West, she succeeded against a government more autocratic than her own. During January the Russian centre in front of Warsaw had been weakened for the sake of movements against the enemy's extreme flanks, which were undertaken in response to requests from the Western Powers in order to divert German reinforcements from France and Flanders. There was a fresh advance towards the Masurian lakes in East Prussia, and far to the south Alexeiev captured a Carpathian pass at Kirlibaba. Mackensen took advantage of this dispersion to organize a strenuous attack on the Russian lines near the confluence of the Bzura and the Rawka. It began on the night of 1 February, and the Russians were on the 2nd and 3rd pressed back from their position on the heights at Borzymow and Gumin. But two railways from Warsaw ran north and south of the threatened front, and reinforcements brought up along them stopped the German advance. It would in any case have been held before the still stronger lines at Blonie which were the real defences of Warsaw on the west, and Hindenburg now gave up the frontal attack as hopeless. It was only, however, to turn to the northern flank and repeat his attempt of October to pierce the great chain of fortresses which defended Poland along the line of the Niemen and the Narew from Kovno to Novo Georgievsk.