Napoleon's most important achievement was establishing the Napoleonic Code, which is used in the United States, and still lives on today in France. Russia's growing anger with France had also started with the continental system, and how Russia wasn't really prospering in that agreement. It really angered Russia's ruler at the time, Tsar Alexander I, when Napoleon took over Duchy of Oldenburg. The ruler of Oldenburg, was Tsar's uncle, and there was many more blood ties within that family. And at the year of 1811, Russia had started preparations for war with France. Napoleon's mistake when invading Russia was that he wasn't prepared. A good 400,000 men dead because of Napoleon. The roadwork in Russia they traveled on was poorly made, food was scarce, the weather and climate kept changing, which was not good for the bodies of the men who were new to the weather.