By 1812 only Great Britain and Russia hold any real opposition to Napoleon, who determines to destroy Russia first and enforce his trade blockade against the British.
In Poland Napoleon gathers the Grande Armee of over 600,000 men drawn from all the states of his empire. As a result of Napoleons previous secret 1808 alliance with Russia the Ottomans refuse to support the proposed French attack on Russia, and as a consequence of Napoleons concentration of troops in the east, Russia ends its long war against the Ottomans. 
This allows 200,000 Russian veterans from the Balkans and Caucasus to move north to fight against the French. In Spain the British, Spanish and Portuguese allies are driving the French back to the Pyrenees.
