The idea of invading Russia was considered as early as 1810 when it became obvious that Alexander I was no longer adhering to the Treaty of Tilsit. He could no longer afford to do so; the blockade was badly hurting both the Russian economy and the tsar's reputation at home.
Four days after crossing the frontier into Russia, Napoleon met with the Russian emperor's aide-de-camp, General Alexander Balashov. He had been sent to explain to Napoleon that there could be no negotiations as long as French troops were on Russian soil. Napoleon's reply was a personal indictment against Alexander. It is obvious that Napoleon felt betrayed, but also that he had misjudged him. It also shows that Napoleon, who was looking for a knock-out blow and who probably had no intention of advancing so far into Russian territory, was still unsure as to what he wanted from Alexander.
I have received Your Majesty's letter. The war which divided our states was ended by the Treaty of Tilsit. I went to the Niemen conference with the resolution not to make peace unless I obtained all the advantages that circumstances promised me. Consequently, I refused to see the king of Prussia there. Your Majesty said to me, 'I will be your second against England'. This remark from Your Majesty changed everything; the Treaty of Tilsit was its corollary. Since then, Your Majesty has wished that modifications be made to the Treaty; you wished to keep Moldavia and Wallachia, and to carry your boundaries forward to the Danube. You had recourse to negotiations. This important modification of the Treaty of Tilsit, so advantageous to Your Majesty, was a result of the Erfurt Conference [September 1808]. It appears that, towards the middle of 1810, Your Majesty wished new modifications to the Treaty of Tilsit. There were two means of arriving at that, negotiation or war. Negotiation had been successful for you at Erfurt; why, this time, did you