Sentence:  ... whether it be natural to the "Indians" to be thus melancholy, or the effect of their Slavery, I am not certain: But I have always been prone to believe, that they are then only <WSD>condoling</WSD> their Misfortunes, the loss of their Country and Liberties ... 
Meaning of the word marked with <WSD> tags:  To lament, grieve, bemoan (something).