Van Gogh's correspondence is collected at this site: http://vangoghletters.org/vg/letters.html
In letter number 612
he complains of the white man's crude treatment of cannibalistic tribes:
"....cannibals in the sense that letís say an individual was eaten once a month, and what of that?
The whites, very Christian, etc., to put an end to this barbarity? really not very savage...., could think of nothing better than to exterminate both the tribe of cannibal natives and the tribe with which the former was at war (in order to obtain the requisite edible prisoners of war on both sides). Then the two islands were annexed, and did they become dismal!!! Those tattooed races, those negroes, those Indians, everything, everything, everything disappears or is corrupted."
Of Gauguin he writes:
"...everything his hand makes has a sweet, heart-rending, astonishing character. People donít understand him yet, and he suffers greatly from not selling, like other true poets..."
Van Gogh bought "Among the Mangoes" for 400 francs.