Did Portugal participate in the slave trade?
Atlantic slave trade
The First Atlantic system was the trade of enslaved Africans to, primarily, South American colonies of the Portuguese and Spanish empires; it accounted for slightly more than 3% of all Atlantic slave trade. It started (on a significant scale) in about 1502 and lasted until 1580 when Portugal was temporarily united with Spain. While the Portuguese were directly involved in trading enslaved peoples, the Spanish empire relied on the asiento system, awarding merchants (mostly from other countries) the license to trade enslaved people to their colonies. During the first Atlantic system, most of these traders were Portuguese, giving them a near-monopoly during the era. Some Dutch, English, and French traders also participated in the slave trade. After the union, Portugal came under Spanish legislation that prohibited it from directly engaging in the slave trade as a carrier. It became a target for the traditional enemies of Spain, losing a large share of the trade to the Dutch, English, and French.
Japanese diaspora
Japanese have lived overseas since at least the 16th century. After the Portuguese Empire first made contact with Japan in 1543, a large scale of slave trade developed in which Portuguese purchased Japanese as slaves in Japan and sold them to various locations overseas, including Portugal itself, throughout the sixteenth and seventeenth centuries. Many documents mention the large slave trade along with protests against the enslavement of Japanese. Japanese slaves are believed to be the first of their nation to end up in Europe, and the Portuguese purchased large numbers of Japanese slave girls to bring to Portugal for sexual purposes, as noted by the Church in 1555. King Sebastian feared that it was having a negative effect on Catholic proselytization since the slave trade in Japanese was growing to massive proportions, so he commanded that it be banned in 1571.