Take the Slavery in the United States as an example, but reverse it all around

This undermines the premise. There is no parallel to the trans-Atlantic slave trade and Europeans' enslavement of black Africans in the early modern/modern era.

Slavery was a fact of life in the pre-modern world, including of "white" western Europeans. /u/textandtrowel is better on medieval slavery than I am. So I will just note that Bede tells us 6th-7th century pope Gregory the Great witnessed slave boys from England being sold at a market on the continent, and when told who they were, remarked on the basis of their pale features "No Angles but angels."

When Christians and Muslims fought each other throughout the Middle Ages, prisoners of war on either side might find themselves as slaves where ransom or execution wasn't an option. Where sources on the two sides express concern over this practice is about women and children (in conquered towns or traveling with the army as camp followers) being kidnapped as sex slaves.

What most people probably think of as historic white slavery is the Barbary slave trade, which is discussed in more depth here. For about a century in the early modern era, corsair captains/pirates from the Barbary city-states in North Africa kidnapped European ship crews and conducted raids along European coastlines. On one hand, they wanted slaves for labor in Algiers and Tunis--farming, construction, the luckier ones might end up in domestic service. On the other, they were out for money. These luckiest-of-all "slaves" were held for ransom, encouraged to write letters back home explaining their situation, could the friars (Catholic) or city council/local parish (Lutheran) just please band together and raise the ransom money so he could come home, thanks.

We know the conditions for the slaves working in agriculture and construction were terrible. Certainly those who were forced to row Barbary galleys were in no better shape. (In contemporary Crete, free people volunteered for sometimes near-certain death in other military positions to avoid being conscripted for naval galley service.) Women and probably children who were swept up in the coastal raids--who were barely 10% of the total slave population, scholars have estimated--might be held for ransom. Or their fate would have been domestic service/sexual slaves.

Was the Barbary slave trade a parallel to white European/Americans' enslavement of black Africans? No. The Barbary city-states allowed, they encouraged their captives to be ransomed back to Europe (and in a couple cases later on, America) for money. Judging by names on the records, 40-60% of corsair captains doing the actual raiding and enslaving were white Europeans who had nominally converted to Islam for profit and marauding. The actual period of enslavement for labor was relatively short, ending in the 17C, although kidnapping for ransom continued and tapered off in early 19C. (ETA) The Barbary trade was not limited to western European slaves. They labored alongside sub-Saharan Africans, eastern Europeans, and perhaps non-Muslim central Asians.

There is no discernible impact on Europe's economy from the (temporary) loss of people, or money paid out in ransom, or even really the hit to company and military coffers from the loss of ships. (This is actually kind of a mystery to historians, leading many to doubt whether the Barbary slave trade was as numerically large as other scholars have calculated.) The trans-Atlantic slave trade represented the systematic, long-term, broad-scale destruction of nations, peoples, and people.

Barbary pirates from the Ottoman empire raided Iceland in 1627 and took several hundred slaves (~400 seems to be the consensus), including the reverend Ólafur Egilsson and his family, who where then shipped back south to be sold. Ólafur later wrote an account of what they experienced. From letters sent back to Iceland and Ólafurs accounts it seems that the slaves where sold to various masters to do various jobs and were treated with varying degrees of respect (all the way from "decently" to "none").

Ólafurs texts were restored and translated recently, and were published in English as "The Travels of Reverend Ólafur Egilsson" in 2008.

Source: The Travels of Reverend Ólafur Egilsson (Reisbók séra Ólafs Egilssonar) Captured by Pirates in 1627. Translated and edited by Karl Smári Hreinsson and Adam Nichols, released 2008.

Hi, thanks for the question. As others have pointed out, there are some problems with the Trans-Atlantic slave trade parallels, but let me take a different tact with this question and look at the early modern period's interaction between Barbary Coast corsairs and American and European prisoners, specifically with the story of James Leander Cathcart.

Mr. Cathcart had participated in the Revolutionary War as a Privateer (tender age of 15 or so) and post-War became a ship captain transporting lumber and other agricultural products to markets in the Mediterranean when his ship was captured by the Barbary Coast Corsairs operating out of Algeria.

Cathcart and his crew were held for ransom, but as low-profile prisoners, their release wasn't happening anytime soon. During captivity, Cathcart was 'selected' to be the personal zoo keeper of the local Dey who, Cathcart reports, ordered that he receive received regular beatings (bastinado) to the point where he permanently lost some of his toenails. However, his treatment, by and large, wasn't nearly that bad consistently; he used that position to learn a smattering of Turkish and Arabic and eventually became a secretary for the very prisons in which his crew were being held.

So far, Cathcart's story seems to be analogous to black slaves in America, but this quickly changes and the analogy falls apart:

He used his position and privilege to pay for better (and more) food for his crewmates as well as purchased a house, hired servants, and even owned a tavern or two. He becomes a highly-trusted and valued translator and advisor to the Dey. Eventually, the United States signed the Treaty of Algiers with the Barbary Coast powers and Cathcart was released as part of the deal. He sold all his Algerian possessions and rounded up his crew, sailing back to America. Cathcart would eventually return to the Barbary Coast as a diplomat, but this is outside the scope of your question.

More to the point of your question; yes, white Europeans/Americans were taken as prisoners (I would hesitate to say "slaves") and treated poorly, but there is really no equivalent to the way that Africans were treated in the Americas. You'll note that Cathcart's treatment was unusual even within the context of his own tale; while he was working, his crewmates languished in a kind of prison awaiting ransom. Indeed, most crews were ransomed in this period and, until the end of the Second Barbary Coast War, this was a common practice; the prisoners were more valuable as ransom than as slaves. More difficult to discern from Cathcart's anecdotal stories is the way in which slaves were treated; physical punishment - even severe beatings - were common in a lot of societies (just try being an offender on one of His Majesty's naval ships) and Cathcart makes these beatings seem random and arbitrary (which they could be, but most likely aren't). Also, Cathcart very quickly comes to secure his own property, had servants of his own, and operated businesses; I cannot think of a single slave in the Americas who has a similar experience before emancipation. All in all, Cathcart's experience is a-typical at best and possibly unique.

If you are interested in reading more about Cathcart, I recommend his book "[The Captives: Eleven Years a Prisoner in Algiers] (https://archive.org/details/captives00cathrich)" which was compiled and printed by Cathcart's daughter well after the ordeal.

A more interesting question, and examination, of poor treatment of "White" slaves would be when Oliver Cromwell invaded Ireland and sent tens of thousands of Irish Catholics into slavery in [Barbados and the Caribbean] (https://youtu.be/PSlOSXZ9TCI?t=531). Irish, for most of modern British history, were barely considered human and so might come closest to poor treatment and slavery that parallels the Black experience in the Americas (but even that falls apart as the Irish integrate, change religion, and move to the provinces).

Do we include sex trafficking in this discussion?