And here's the explanation:
The Catholic Church is not in fact a Christian organisation. It is a continuation of the Roman pagan cult of sun worship, actually a continuation of the Roman Empire itself.
It was created by Emperor Constantine, an outright pagan, who remained an outright pagan all his life, even after his supposed 'conversion', which was in fact a political ploy to gain spiritual and so better political control over the fragmenting and dissolving Roman Empire. It worked, and within a couple of centuries the Empire was re-established as the Catholic Church under political Emperor Charlemagne.
"And in US (America) slavery was condoned by nearly all forms of non-Catholic Christianity save Quakers, who were a minority among Protestants."
Sorry but this is not born out by any evidence. Protestants, especially puritan New England, were always staunchly against slavery, to the extent that there was a strong secession movement within New England itself in the antebellum period, as they did not want to be part of the same country with slave-holders.
"If you do not believe those countries or America was founded on Christianity then you are in the minority view"
Then thank God we live in a society where there is not a democratic tyranny of the majority, as I believe that view is the right one.
Obedience to God is resistance to tyrants.