Bli först att boken Serfdom and Slavery.
These organizational conditions explain historical episodes that Domar accounted for, those he left unexplained, and imply that serfdom and slavery are mutually exclusive.
Bli först att boken Serfdom and Slavery.

I. Comparison of Serfdom and Slavery
The Third Census of the Russian Empire (1762-1766) provides uswith the estimates of the extent of bondage; in all probability,fully seven-ninths of the Russia population was unfreeat this time. Notably, at least 40% of these serfs and slaveswere ; (the percentage swelledafter the state nationalized the land and serf holdings of theOrthodox Church). Serfdom and slavery did gradually decline inimportance, but extremely slowly, as these additional censusesreveal:
The Emancipation of Serf and Slave in Russia and America
While the other nations of Europe were gradually abolishing serfdom,Catherine the Great was extending it in Russia. Serfdom and slaverystill existed in Russia in 1839 when de Custine wrote his ,and was not officially abolished until 1861. Nor was this a marginalinstitution; servile labor was the norm, not the exception.

I enjoy your blog but don’t know why you equate serfdom with slavery (and serfs with slaves.) Both serfdom and slavery were evil institutions, but they were not the same. As bad as it was for the serfs, by and large serfs had more autonomy than slaves. Serfdom was terrible and unjust, but slavery was even worse. This is not “merely a matter of semantics.”In Western and Central Europe from the seventh to the ninth century, peasants were by birth personally or legally and administratively dependent on seigniors. With the exception of manor serfs and slaves settled on holdings, however, they were not bound to the soil or to the person of the seignior by law and were not subject to the other restrictions of serfdom. Only under Charlemagne, during the short-lived ascendancy of the Frankish state, were attempts made, generally without success, to bind a larger segment of the peasantry to the soil. At that time peasants were legally attached to the land only in southwestern Europe, on the territory of the former Roman Empire.