Napoléon did not conquer for the thrill of it. With the failure of the Peace of Amiens, it was clear that the struggle between Revolutionary/post-revolutionary France and Britain could only be ended by the victory of one of these two. As Napoléon had no navy up to the Royal Navy, his only shot at downgrading the British was economical war, hence the continental system, aiming at strangle the british trade. If not, the British would continue to fund coalition after coalition sent after France. So he did not have many choices but to enlarge his control zone. The real question is how. Had Napoléon not tramping on his "allies" feet, but actually worked with them to build a real alliance, things might have ended different. For example, with the British intervention in Portugal, a french action was inevitable, but seizing the Bourbons and putting his brother on the throne was a very bad move. With no Spanish insurrection, could Wellington hold on into Lisboa ?