Very Busy Front- What Do You Think?

I saw this cover front on ebay recently, and was wondering more about it- why did they use a 'parcel post postage due'?

Where was this mailed from (it appears to have an English cancel?)

And, what's it worth?

I'll hazard a wild guess. The sender is military 'on active service'. The blue stamp says Doorgelaten, which google translates as 'passed' in Dutch, so that could be a military censor stamp. I think the postage due stamp, over the censor stamps reads 'due 20 cents' from the New York postal station, though it could read 10 cents, it is blurred.
If the date is 1915 (next to censor stamp), during war time, perhaps the post office was short regular postage due stamps and used a handy parcel post due instead?
So I guess what I'm saying is military mail sent from Europe to US, since the US wasn't in the war yet, they didn't recognize the military franking and charged post due.
Does that make ANY sense???

Nice cover, anyway. And I really like the U.S. of N. America.

Beginning July 1, 1913, Parcel Post Postage Due Stamps were valid for use as regular postage due stamps. In the case of the cover scanned, the date appears to be 1915 and postage due amount appears to be 10 cents, so a parcel post postage due stamp was applied to verify payment of the amount of postage due.

This may be a piece of package wrapping, not part of a "cover," and thus the stamp makes sense.

It is a cover front without postage. The letter rate would have been double postage due which would have been 10 cents. I have a few covers mailed from British armed forces that where sent without postage to the USA and were charged postage due because the "free" franking privilege only applied to their domestic mail or to mail to their home country. Another instance would be charging 4 cents postage due for a postcard with double deficiency times 2 cents (converted to US currency). Parcel post postage dues were valid for letter mail at that time as wt1 replied.