Denmark was a staunch ally of France throughout the Napoleonic Wars and was duly punished during the war by the British (who bombarded Copenhagen) and afterwards at the Congress of Vienna, being forced to swap Norway for Swedish Pomerania.
All of this makes me wonder whether things could have happened very differently…
What if Denmark had changed horses at some point during the wars, preventing the destruction of the fleet, and ensuring that the sound wasn’t blocked by the British, thus ensuring that Sweden could have been attacked more efficiently while they were at war with Russia over Finland? And what if Sweden had been less volatile, ending the war on the wrong side and thus being less fortunate at the Congress of Vienna?
Could we have seen Denmark conquer Scania and Blekinge during the war, and demanding Bohus and Halland back at the Congress? Perhaps even getting present-day Gothenburg to make Norway and Denmark meet? A clever Danish king might have traded in Holstein (but keeping Schleswig) in return, thus preventing the war of 1864 (but Sweden would have lost this around that time instead).
It would have been a very different Scandinavia today: A big Denmark-Norway, all speaking one language, and a small Sweden, but probably more densely populated than today.