By annexing Oldenburg, Napoleon virtually alienates Tsar Alexander,
since the heir apparent to that Duchy is his brother-in-law, and
the annexation violates Treaty of Tilsit (July 1807)
Citation:
Editors. "Napoleon annexes Oldenburg".
The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=13649, accessed 26 May 2013.]