In Frederick William IV's eyes, this was a war between Prussia—or rather, the German Confederation—and Denmark.
But in reality, Britain, Russia, and Sweden had all voiced strong displeasure, and even France was planning to get involved.
The British did not want the Prussians breaking out of the Baltic Sea, while the Russians had ambitions of their own in Schleswig. It had the ports Russia dreamed of.
Denmark also controlled the throat of the Baltic Sea. Whether for their own strategic needs or their ambitions for global supremacy, neither Britain nor Russia would give up this place.
Russia in particular had deep ties to the region. The Tsar himself even held titles in Schleswig-Holstein and Oldenburg.
In theory, this gave Russia the possibility of acquiring the region. Naturally, the Tsar did not want the powerful German Confederation or Prussia to take it.
By comparison, it better suited Russia's interests for this region, full of contradictions, to remain under the rule of Denmark, a feeble suzerain.
From the standpoint of both strategic offense and defense, Sweden could not tolerate Prussia or Germany laying claim to Danish lands.
Denmark was the only direction in which Sweden might expand at the time, and the two countries were bound together like lips and teeth. It certainly did not serve Sweden's interests to let a great power occupy Jutland.
Denmark coveted Norway, but its national strength had waned. Its navy, in particular, had never recovered in the decades since the British destroyed it. Its fiscal deficit was severe, and it had even been forced to sell its colonies to weather the crisis.
The Kattegat Strait, the Sound, the Great Belt Strait, and the Little Belt Strait—Denmark controlled every waterway into the Baltic Sea.
If these vital waterways changed hands, Sweden's maritime economy and security would be