Maybe Napoleon II doesn't die of tuberculosis and is able to live longer. Let's say that in awe of his father he studies military tactics seeking to emulate his father and serves under the Austrians earning a reputation as a successful military commander. But during the 1830's Austria is crippled by revolts and revolutionaries allowing for Napoleon II to escape his gilded cage and flee to Italy. He was crowned by Napoleon I as King of Rome, and never formally abdicated his title along with his French Imperial title. Perhaps he travels to Lombardy-Venetia with some Austrian troops that defected to him and raises a rag-tag army to reclaim his Crown. In this alternate timeline Napoleon II is just as good of a commander as his father and is able to steamroll through Northern Italy. Seeing his many victories, some Italian nationalists begin to flock to him swelling his numbers. Perhaps he could make a deal with the Pope who acknowledges his claim to Italy in exchange for keeping the Papal states intact with Italy united in a more federal model. Then the Pope then takes the Iron Crown of Lombardy and formally crowns Napoleon II as the rightful King of Italy. In his Italian campaign he meets up with his cousin Louis-Napoleon (Napoleon III) who was involved with Italian revolutionaries in his youth in otl. Napoleon II likely steamrolls Southern Italy conquering the Kingdom of Two-Siciles. Though an alternate option is for him to have Louis-Napoleon marry a Sicilian Bourbon Princess and appoint him regent of Italy or as a puppet King of Naples/Two Siciles.
News of Napoleon II's stunning victories shocks Europe but they have other things on their minds as revolution is breaking all throughout Europe. Perhaps as a Butterfly event the reign of George IV the Queen Caroline affair is worse and combined with the Liverpool government, Britain becomes unstable and intervening in Europe is the last thing on its mind as tensions between the Liberal government and the King are rising. Perhaps in Prussia all this revolutionary fervor causes more revolts there with many Pan-Germanic movements calling for a united Germany. The July Revolution would occur with the out of touch Charles X becoming very unpopular with the French. Louis-Philippe who was the last King of France also grew unpopular while Napoleon II was busy conquering Italy. And with the Pope backing the Napoleon II he then prepares to launch a coup against Louis-Philippe who many in Paris saw as a tyrant. Through the use of shrewd politicking, Napoleon II presents his campaigns in France as similar to that of his Father. He presents himself as a just ruler and pro-Bonaparte press begin talking about the glories of the Empire compared to the tyrannical and stagnant Ancien Regime. Napoleon II then waltz into France and many troops defect en masse to him. Some of the old peerages in France also support him as many military families were made into Imperial Nobility by Napoleon I. Napoleon II reclaims his title and Crown as Emperor of the French and King of Italy and proclaims the restoration of the French Empire. He then presents himself as a man to restore stability and France's Imperial Glory. With Louis-Napoleon's influence he begins on a similar reconstruction of Paris and adopts a policy of neutrality to build up France's economy and military. With his experiences in fighting in Austria and Italy he then rebuilds France's armies and integrates his Italian troops with his Imperial army as Italy would be treated as an equal partner to France. Napoleon also grants his Italian supporters Imperial noble titles and positions in government to keep them happy and and content. And with the divided nature of the revolutionaries, Europe manages to eventually put down rebellion after making some toke concessions much like otl with states like Prussia and Austria forced to adopt a Constitution. Russia would also be plague with revolts but these are brutally crushed by the Tsar. Austria however isn't so lucky as the Hungarians would seek to break away from it after Napoleon II successfully broke off Italy from the Austrians. Lombardy-Venetia was also one of the richest provinces of the Austrian Empire and the loss of it would cause a crippling blow to the Hapsburgs. They appeal to Napoleon II who is half Habsburg to intervene which he does, demonstrating France's revived martial vigor.
In 1848, the Frankfurt convention is called much like otl, but the revolutionaries are more emboldened by the weakness of the Austrians and Prussians. And as a result it manages to push for a general unification of Germany. Of course since the Prussians are more dominant the Crown would be offered to the Hohenzollerns. For the sake of this scenario, a more liberal king is in charge of Prussia. Perhaps Frederick Wilhelm is forced to abdicate to a more liberal relative. Of course seeing weakness in Germany Napoleon seeks to expand and gobbles up territory in the Rhine gaining France's natural borders. Of course this angers the German revolutionaries which causes relations to strain with the French. Perhaps Napoleon III marries a Bavarian von Wittlebach Princess and the Bavarians and Austrians secretly appeal to Napoleon II as they don't want to be under the Prussian yoke. Perhaps the reactionary Russia allies with France in opposition to a united and liberal Germany on their doorstep. War erupts as Germany tries to retake back some portions of the Rhineland. Of course with Napoleon II being a good military commander is able to successfuly lead France into victory. Because the revolutionary movements were more protracted in Germany, Prussia's army would be in disarray while France would be fresh with its rebuilt army and booming economy thanks to it being spared the chaos of the rebellions and revolutionary movements. The Frankfurt united Germany then collapses and Napoleon II forces the independence of Bavaria and maintains the independence of Austria. Perhaps the Austrians are given parts of Silesia as compensation while Germany is forced under the re-established Confederation of the Rhine. Bavaria would receive some territory and perhaps Westphalia will be restored to a kingdom under the von Wittlesbachs as well. Prussia would likely be dismantled by Napoleon II and permanently weakened with the loss of so much territory. Perhaps Napoleon revives the Grand Duchy of Warsaw from Prussian lands. Perhaps he'll appoint his Polish half brother Alexandre Walewski as Grand Duke to create a Polish cadet Branch of House Bonaparte. Napoleon II would then work to try and integrate his conquests and alliances, but for many decades his German dominions would likely be unstable as he would have to prop up his German allies.
) would be the only politician capable to change for the better the critical decade of the 1860s, to avoid the unholy parliamentarian alliance of the Sardinian most retrieve aristocracy with the equally despicable great landowners from southern Italy and to keep the king under control.
