The Crimean Khanate maintained a massive slave trade with the Ottoman Empire and the Middle East until the early eighteenth century. In a series of slave raids euphemistically known as the "harvesting of the steppe", Crimean Tatars enslaved East Slavic peasants. The Polish–Lithuanian Commonwealth and Russia suffered a series of Tatar invasions, the goal of which was to loot, pillage, and capture slaves, the Slavic languages even developed a term for the Ottoman slavery (, based on Turkish and Arabic words for capture - "esir" or "asir"). The borderland area to the south-east was in a state of semi-permanent warfare until the 18th century. It is estimated that up to 75% of the Crimean population consisted of slaves or freed slaves. The 17th century Ottoman writer and traveller Evliya Çelebi estimated that there were about 400,000 slaves in the Crimea but only 187,000 free Muslims. Polish historian Bohdan Baranowski assumed that in the 17th century the Polish–Lithuanian Commonwealth (present-day Poland, Ukraine and Belarus) lost an average of 20,000 yearly and as many as one million in all years combined from 1500 to 1644.