Not completely accurate. The latter is 100% accurate yes, but the former, no. For 'Americans' if we extend the history back as being times from say 2000 BC to now, then 'Americans' have practised slavery. We as a nation however are a young nation, and we only had slavery for the first century of our nation's life and then abolished it completely -- better than most countries, yes.
however, in the case of Europeans slavery was commonplace before Christianity -- think of the Spartans and their slave society etc. Athens had 60% or more of it's population as slaves
In the medieval world only the rich lands: the Byzantines and Moslem lands could afford slaves.
As the Black Death killed much of the population, the cost of slave labor increased.
Note that in the Domesday book compiled by William the conqueror in 1086, nearly 10% of the population of England were slaves. The trade of slaves was made illegal in England by the 12th century. the Scandanavians had thralls
the world as a whole did not actively stop slavery until the Methodists came along -- and in the 1800s only.
Also, the Methodists were only one of many anti-slavery sects. The Congregationalists (direct descendants of the Puritans) predated them.
And, yes, slavery did indeed survive the fall of the Western Roman Empire in 476 a.d., but it did not thrive and spread until the introduction of Islam some two centuries later.
Further, it is also true that Native American tribes practiced slavery before the white man arrived. Like our ancient Greek, Roman and Old Testament era forebears, they saw it as a humane alternative to what it had replaced-- wholesale genocide of conquered civilizations.
Slavery took a new twist once the Spanish arrived and found native peoples did not work willingly as slaves, particularly when compared to the growing supply from Africa. It was only natural that later colonizers, including the English, did the same. The first Europeans to trade in African slaves were, of course, the Portuguese who, of course, were also the first explores of the dark continent. Guess who supplied them with slaves?
Speaking of slavery among Native Americans, even as America expanded west, some of our tribes quickly learned to trade on the sympathies of whites opposed to slavery. There was a commonality of Quakers settling Pennsylvania, Methodists settling Kansas and Mormons settling Utah whereby local tribes learned to take slaves from rival tribes and sell them to the anti-slavery settlers (who would try to convert them and set them free) as a type of shakedown racket not so different than modern liberals exploiting certain favored minority groups for political power.
Pagans will do anything. I'm talking about European civilization, which dates from its conversion to Christianity—as early drafts of even the EU Constitution pointed out. Measured in historical time, Christian Europeans were mere dabblers in slavery. This should be no surprise, since it is Christian philosophy, and only Christian philosophy, that opposed slavery and sparked its abolition in most places.