On the 30th of December, the Prussian General Yorck, who led the Prussian corps serving previously under Macdonald in Courland, concluded the Convention of Tauroggen with the Russians, stipulating that this corps should hold the district around Memel and Tilsit as neutral territory, until Frederick William's decision should be known.
Strictly considered, this convention was a grave breach of international law and an act of treachery towards Napoleon.

The King at first viewed it in that light; but to all his subjects it seemed a noble and patriotic action.

To continue the war with Russia for the benefit of Napoleon would have been an act of political suicide.
Yet, for some weeks, Frederick William waited on events; and these events decided for war, not against Russia, but against France.

The Prussian Chancellor, Hardenberg, did his best to hoodwink the French at Berlin, and quietly to play into the hands of the ardent German patriots.

After publishing an official rebuke to Yorck, he secretly sent Major Thile to reassure him.