The crushing Central Powers’ victory over Russia at Gorlice-Tarnow cleaved through the eastern front. With German armies simultaneously advancing along the Baltic coast, the Russian High Command feared encirclement if they concentrated their forces in defence of Poland and retreated rapidly. Eventually, they tried to consolidate behind the Bug River, but left Warsaw and the nearby fortress of Ivangorod isolated. At the beginning of August, the German 12th Army seized Ivangorod and Warsaw, now defenceless, was occupied on 5 August. The Russian retreat continued, with the Central Powers occupying the whole of Lithuania and the key fortresses of Novo Georgievsk and Brest-Litovsk. By this stage, the armies of the Central Powers were exhausted, depleted and disease-ridden; the great advance was halted at the close of the campaign season with the capture of the Lithuanian capital Riga on 19 September.
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