Supposedly, during the French Consulate the Count of Artois, or someone else, offered Napoleon the title Grand Constable of France if he would support a Bourbon restoration. The Grand Constable was a position that had not been used in a few hundred years. This would have made Napoleon second only to the king in military matters and one of the most powerful people in the kingdom.
What would be the internal and external consequences of such an action?
First of all, it is important to remind that this can happen only if Louis XVIII acts in a very different way than he did OTL. Which means that he and Napoleon would both be different persons, because Bonaparte did not want to be a mere George Monck. He wanted to rule France.
And Louis XVIII just wanted to be restored as king and to rule the men he would name to govern France.
This won’t happen.
Napoleon will not make a deal with Louis XVIII on lesser terms than himself being a kind of Mayor of the Palace, or Shogun, or a super-Richelieu that can’t be removed. And Louis XVIII was definitely not ready to accept it in 1800. It took him 14 more years to accept much less than this.
Making such a move as restoring Louis XVIII is shooting one’s silver bullet. And there is but one such silver bullet to shoot for a Statesman. So Napoleon, who was the most ambitious man of his age (could anyone imagine an obscure Corsican noble making himself emperor of France and master of Italy ?) will of course calculate if such a restoration will last or if it is doomed.
France’s political culture was considerably different in 1800 from what it had been in 1789/1792. And Louis XVIII, although much more politically acute than his brothers, however was still not enough in touch.
This being said, let’s suppose that Louis XVIII has a road to Damascus experience and accepts the political principles of the French Revolution in order to be restored as a constitutional king of France.
Napoleon is chosen as Head of government and head of the army.
They both will have a tough ride.
On the home stage because there will be political unrest from the jacobin revolutionaries.
Napoleon will probably quickly lose a large part of his political credit because there was not a strong demand for a monarchical restoration in French public opinion. What the French wanted was the return of order and prosperity at home in the respect of the new principles established by the French Revolution (which Napoleon gave them and which explains Napoleon’s enduring popularity in France). But this will anger the real republicans, at least the staunchest ones. And republicanism was strong in the army. Napoleon, once in power, always had the support of the army because of his military prestige and victories, but at the start also because he was a crowned republican, a crown moderate revolutionary that wanted order at all costs.
On the diplomatic field, France still needs to make peace since it is at war with a large part of Europe, and first of all Austria and Britain.
France has a good prospect to secure its 1800 frontier, that is present day frontier plus Rhineland plus Geneva.
If it is not to be a mere truce as the treaty of Amiens OTL was, the price for this will be to restore a free republic or kingdom of Holland, probably to restore the House of Savoy on a really independant kingdom in northern Italy (the house of Savoy was a close ally of Louis XVIII, whose wife was a Savoy).
Then, there will probably be in a few years a conflict between France and the US because France will then have much more means to settle Louisiana. One can even imagine France buying California from Spain and getting all the Pacific coast up to the bay of Vancouver.
