you would have to put this at the beginning of the sentence

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Note added at 34 mins (2012-07-24 19:37:22 GMT)
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or

justifiable explanation

the latter!

slight rearrangement needed

Perhaps something like this might be an option.

This unprecedented/heretofore unknown situation finds (its) rightful justification in the...

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Note added at 16 hrs (2012-07-25 11:07:45 GMT)
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I'm not so sure what AllegroTrans finds so cumbersome; that said, perhaps "rightful" or "fitting" could be eliminated, i.e., "...finds its justification in..." (as seen below). This phrase is quite common in formal discourse (as the thousands of Google hits clearly suggest).

Trade Secrets and th Justification of Intellectural Property
http://cyber.law.harvard.edu/IPCoop/91pain.html
After rejecting several rationales for intellectual property, Hettinger **finds its justification in** an instrumental, or "utilitarian,"3 argument based on incentives...

"finds its justification in"
About 219,000 results (0.38 seconds)
https://www.google.com/search?q="finds its rightful justific...

This unprecedented situation finds its justification/reason for being in the very characteristics of the regimen that came to power in 1978, as it relates as much to xxxx as it does to yyyy

I might be wrong (hence the low level of confidence), but perhaps something like might be an option.