What was napoleon's most important act? andwhy did napoleon invade russia? what was his mistake?

Napoleon's most important achievement wasn't even military related. It was reorganizing the French government and 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. But after second thoughts and other countries wanting to ally, Russia decided to not war with France. But for some reason, Napoleon wanted to war with Russia. And let me just quote Charles ‘One is left, then, with one explanation, and one explanation alone: frustrated by the long war in Spain and Portugal, and the failure of the Continental Blockade to bring the British to heel, Napoleon was simply bent on flexing his military muscle and winning fresh glory'. 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. 

The case was a u.s. supreme court decision that defined the scope of the u.s. congress's legislative power and how it relates to the powers of american state legislatures. the dispute in mcculloch involved the legality of the national bank and a tax that the state of maryland imposed on it.