Napoleon's Continental blockade, or Continental system, as it is often known, was not a blockade as such, but an embargo on British trade goods. It was an attempt to hurt Britain economically and take advantage of Napoleon's military dominance on the continent. Napoleon tried, through the Berlin and Milan Decrees, to force all of the nations on the Continent to close their ports to British goods or face military action. The Continental System was ultimately ineffective because the British navy maintained control over the seas, making enforcement impossible. Additionally, it was far more harmful to the continental economy than it was to that of Great Britain. The refusal of Portugal and Russia to abide by the system was one of the reasons for Napoleon's disastrous campaigns in the Iberian peninsula and Russia.
It shows once more that the power ON THE SEA is stronger than the power ON THE CONTINENT.
Roma and Carthago;
France of Louis the XIVth against Great Britain in the seventeenth century;
Germany against Great Britain and the USA during the WW I;
Germany once more occupying almost the whole Europe during WW II