You will start the campaign as British take a small foot hold in Southern Europe. Unfortunately for Napoleon, Portugal who were allied with the British were still holding out against French attacks for the time being. He wanted to close Europe off to the British who were one of the biggest threats to French territory and trade. Napoleon had managed to take a large chunk of Europe for France. This campaign was predominantly between Napoleon of France, the British Empire, Spain and Portugal.
Napoleon: Total War is getting a new expansion pack based around the Iberian Peninsula campaign.