The homeland of the primitive nucleus of this branch of the Indo-European family is restricted in the main to the plains extending from the northwestern corner of the Black Sea to the sandy delta of the Oder. The valleys of the great rivers in this lowland exerted the earliest separative influence which is known to have occurred in the primitive Slav group. Niederle distinguishes three main sub-groups which fit into the frame of eastern European hydrography.[130] A northwesterly branch attained the valleys of the Elbe, Sale and Sumava, and gave birth to the Bohemian and Polish factions. A central group, originally occupying the region of the upper Vistula, the Dniester and middle Danube, rounded the southern slopes of the Carpathians and, traveling up-stream on the Danube, eventually attained the valleys of the Save and Drave. The Slavs of southeastern Europe are descendants of this group. Originally pure Slavs, they are permeated with Asiatic blood owing to repeated invasions from the east. The third group was destined to form the substratum of Slavic Russia. It radiated from the basin of the Dnieper as far north as the Gulf of Finland and eastward to the valleys of the Oka, the Don and the Volga. TABLE I FORMER POLISH PROVINCES UNDER GERMAN RULE AT THE BEGINNING OF THE EUROPEAN WAR[131] Period of Area in Population loss to PROVINCE sq. mi. 1910 Poland POMERANIA, regencies of Strzalow (Stralsund), Szezecin (Stettin), XIIIth and Koszalin (Köslin) 11,751 1,716,921 century[132] WEST PRUSSIA, regencies of Gdansk (Dantzik) and Kwidzyn (Marienwerder) 9,966 1,703,474 1772[133] EAST PRUSSIA, regencies of Krolewiec (Königsberg), Glombin (Gumbinnen) and Olsztyn (Allenstein) 14,431 2,064,175 1656[134] POSNANIA, regencies of Poznan (Posen) and Bydgoszcz (Bromberg) 11,307 2,099,831 1815[135] REGENCY OF FRANKFURT XIIIth (Francfort-sur-l’Oder) 7,487 1,233,189 century PROVINCE OF SILESIA, regencies of Lignica (Liegnitz), Wroclaw (Breslau),[136] and Opole (Oppeln) 15,731 5,225,962 1335 SAXON DISTRICT OF XIIIth BUDZISZYN (Bautzen)[137] 963 443,549 century TABLE II POLISH ADMINISTRATIVE DIVISIONS UNDER AUSTRO-HUNGARIAN RULE AT THE BEGINNING OF THE EUROPEAN WAR Area in Period of loss TERRITORY sq. mi. Population to Poland MARQUISATE OF MORAVIA 866 2,622,271 XIth century DUCHY OF SILESIA[138] 2,007 756,949 --