Okay, the causes are relatively simple, the Napoleonic Wars were caused by the French Revolution. After years of excesses caused by the French Revolution, Napoleon rose to establish some measure of peace and stability in France. The Wars of the Revolution were still raging however and its hard to tell if Napoleon originally intended all of Europe to fall under his sway, or if that came later. Anyway, in trying to secure his and France’s position and later expand his position he ultimately came to fight all of the great powers in Europe.
As for the effects of the wars. Okay, Congress of Vienna essentially established 19th century Europe, planting the seeds of nationalism in Germany and Italy. The Holy Roman Empire was gone, most of the smaller weaker German principalities were also gone. Austria declared itself an empire in its own right (The monarch of Austria was almost always Holy Roman Emperor). This set the stage for Prussia to become the dominant state in what we now think of as Germany. Over time both Germany and Italy would consolidate into the nation states we know today.
Further afield, Napoleon sold America the Louisiana Territory, Brazil, after years of being the seat of the Portugese Empire decided it would prefer be independent than be just a colony of Portugal. Likewise, a number of Spanish colonies would gain independence during the Napoleonic Wars or in the aftermath.
