Prosperity repined the principle of decay?

[Ksguo]

In his ‘The history of the decline and fall of the Roman Empire’，Edward Gibbon writes：‘…The decline of Rome was the natural effect of immaterial greatness．Prosperity repined the principle of decay；the cause of destruction multiplied with the extent of conquest；…’
I can not quite understand the meaning of ‘repine’in this context．I looked up many dictionaries，online or printed，only to find none of them gives its definition when it is used as a transitive verb．So I need help．Thank you．
By the way，in ‘The Eastern part of the Empire －Known as the Byzantine Empire to modern scholars，but Roman as far as they were concerned－…’，to whom does the word‘they’refer？modern scholars？I think it refers to Romans，but can’t be sure.

[Cerberus™]

- To repine was in fact also used transitively before modern times; Gibbon wrote in the 18th century.

- I believe "they" are the Romans, as you say. Gibbon's use of the pronoun is somewhat sloppy here. He could have written "as far as it was concerned", but that would not have been very elegant either.

If you need to know more about this text, please edit your message by adding the correct punctuation marks, as it is somewhat hard to read now. I see odd characters where punctuation marks should be.