In many of the Baltic countries, slavery was starved out of society by Christian influences. When the Teutonic Order and Livonian Sword Brothers were conducting their respective crusades throughout that region, part of subjugating the pagan population was converting them to Christianity. Those who became Christian (under duress or otherwise) were guaranteed specific rights (in theory, since the crusaders often violated them) relating to slavery, property ownership, inheritance of land, so on and so forth. Ownership of Christian slaves was strictly forbidden in these Orders (not necessarily in Christian lands, since the Poles still held niewolni in neighboring lands), so in some cases, we have instances of Teutonic Order knights denying conversion or deeming it illegitimate to keep personal slaves from the pagan population. Those who formally converted and were accepted as Christian, however, were essentially exempt from being held as slaves. The nobility among the local pagans, once Christianized, could no longer hold slaves (or shouldn't have been holding them, legally). This, as you might imagine, immediately reduced the slave-holding population of the Baltic region. Slavery was replaced by the standard model of feudal land ownership and serfdom (perhaps most well-documented in Estonia), particularly when German settlers arrived and were granted fiefs and became the majority of the vassals throughout these regions for the Monastic State of the Teutonic Order. It's important to note, however, that while slavery should have been abolished by the church's decrees and policies, theory and practical application don't always mix - slavery, according to Toivo Raun's writings on Estonian history, persisted in significantly diminished amounts through the fifteenth century.