The heir to this duchy had married Alexander's sister, whose hand Napoleon had claimed at Erfurt.
The duke, it is true, was offered the district of Erfurt as an indemnity; but that proposal only stung the Czar the more.

The deposition of the duke was not merely a personal affront; it was an infraction of the Treaty of Tilsit which had restored him to his duchy.
A fortnight later, when as yet he knew not of the Oldenburg incident, Alexander himself broke that treaty.[247] At the close of 1810 he declined to admit land-borne goods on the easy terms arranged at Tilsit, but levied heavy dues on them, especially on the _articles de luxe_ that mostly hailed from France.

Some such step was inevitable.
Unable to export freely to England, Russia had not money enough to buy costly French goods without disordering the exchange and ruining her credit.

While seeking to raise revenue on French manufactures, the Czar resolved to admit on easy terms all colonial goods, especially American.

English goods he would shut out as heretofore; and he claimed that this new departure was well within the limits of the Treaty of Tilsit.