What does the following mean in simple English?

"In our time Pius VII, moved by the same religious and charitable spirit as
his Predecessors, intervened zealously with those in possession of power to
secure that the slave trade should at least cease amongst the Christians. The
penalties imposed and the care given by Our Predecessors contributed in no small
measure, with the help of God, to protect the Indians and the other people
mentioned against the cruelty of the invaders or the cupidity of Christian
merchants, without however carrying success to such a point that the Holy See
could rejoice over the complete success of its efforts in this direction; for
the slave trade, although it has diminished in more than one district, is still
practiced by numerous Christians. This is why, desiring to remove such a shame
from all the Christian nations, having fully reflected over the whole question
and having taken the advice of many of Our Venerable Brothers the Cardinals of
the Holy Roman Church, and walking in the footsteps of Our Predecessors, We warn
and adjure earnestly in the Lord faithful Christians of every condition that no
one in the future dare to vex anyone, despoil him of his possessions, reduce to
servitude, or lend aid and favour to those who give themselves up to these
practices, or exercise that inhuman traffic by which the Blacks, as if they were
not men but rather animals, having been brought into servitude, in no matter
what way, are, without any distinction, in contempt of the rights of justice and
humanity, bought, sold, and devoted sometimes to the hardest labour. Further, in
the hope of gain, propositions of purchase being made to the first owners of the
Blacks, dissensions and almost perpetual conflicts are aroused in these regions."