Sentence:  ... let us suppose a small number of persons settled in some sequestered part of the earth, unconnected with the rest .... In this state of natural liberty, society will be their first thought. A thousand motives will excite them thereto, the strength of one man is so unequal to his wants, and his mind so <WSD>unfitted</WSD> for perpetual solitude, that he is soon obliged to seek assistance and relief of another, who in his turn requires the same. 
Meaning of the word marked with <WSD> tags:  Not suited, not fit ("for" something).