The history of Germany in the 12th and 13th centuries is one of ceaseless expansion. A conquering and colonizing movement burst across the river frontiers into the swamps and forests from Holstein to Silesia and overwhelmed the Slavic Wendish tribes between the Elbe and the Oder. Every force in German society took part: the princes, the prelates, new religious orders, knights, townsmen, and peasant settlers. Agrarian conditions in the older German lands seem to have favoured large-scale emigration. With a rising population, there was much experience in drainage and wood clearing but a diminishing fund of spare land to be developed in the west. Excessive subdivision of holdings impoverished tenants and did not suit the interests of their lords. Sometimes also, seignorial oppression is said to have driven peasants to desert their masters’ estates. They certainly found a better return for their labor in the colonial east: personal freedom, secure and hereditary leasehold tenures at moderate rents, and, in many places, quittance from services and the jurisdiction of the seignorial advocate.

The colonists brought with them a disciplined routine of husbandry, an efficient plow, and orderly methods in siting and laying out their villages. Very soon, even the Slavic rulers of Bohemia (now in the Czech Republic) and Silesia (now in Poland) were competing for immigrants. First and foremost, however, the princes of the Saxon and Thuringian marches sought to attract settlers for the lands that they had conquered and the towns that they had founded to open up communications and trade routes. The older regions of the Reich, moreover, had not only peasants but also men of the knightly class to spare—soldiers who needed fiefs and lordships to uphold their rank. Both could be gained beyond the Elbe under the leadership of successful princes. The Germanized east thus became the home of fair-sized principalities in the 13th century, while all along the Rhine River valley the rights of government were scattered over smaller and less compact territories. The Ascanian dynasty, for instance, which under Albert I (Albert the Bear) began to advance into Brandenburg, by 1250 not only ruled over a broad belt of land up to the Oder River but, having already established its control on the Oder’s eastern banks, was ready for further advances. Farther south the Wettin margraves of Meissen busied themselves with settlements and town foundations in Lusatia.

For a time Henry the Lion, as duke of Saxony (1142–80), overshadowed all these rising powers, and the Welf profited as much by the ruthless use of his resources against weaker competitors as by his own efforts in Mecklenburg. As his was the only protection worth having in northeastern Germany, the newly established Baltic bishoprics were at his mercy, and he alone could attract the traders of Gotland to frequent the young port town of Lübeck, which he extorted from one of his vassals in 1158.

The Reich, too, possessed demesnes in the east, notably the Egerland, Vogtland, and Pleissnerland in the Thuringian march. The Hohenstaufen kings therefore took some part in opening up these regions. They, too, founded towns and monasteries on their thickly wooded lands and established their ministeriales as burgraves and advocates over them. But in this, as in many other things, they only competed with the princes. They did not and could not control the eastward movement as a whole.