(originally posted by a now banned member 5+ years ago)
US-Danish War of 1855
The sound controlling access to the Baltic sea is held as a right by the King of Denmark, right to the Swedish shore. By treaty access is unrestricted, but all ships pay a toll directly to the Danish King.
In 1855, the US announced that they were no longer going to pay the toll, and the Danes prepared for war to defend their rights, being fairly confident.
Denmark eventually acquiesed due to fear of the German states to the south to the US buying free passage in perpetuity for a one off payment.
What if the Danes had held their position, and fired upon US ships illegally entering the sound?
The US would most likely declare war (obviously

)
This is followed by US seizes Danish shipping in American controlled waters, and most likely an US occupation of the Danish Virgin Island.
After that, probably not much as neither part is capable of projecting any real amount of power against the other.
After some time a peace is negotiated, were US probably gets the Virgin Islands, but OTOH must pay a hefty sum as companzation for this and access to the Baltic.
I would assume a war between the United States and Denmark is going to be a largely naval affair, IIRC the American Navy is not very strong at this time, but could be built up into a respectable force given sufficient time. Assuming the US is willing to commit the time and money needed for a proper naval buildup, Denmark is probably not going to win the war. I doubt the rest of Europe would be inclined to get involved, and other nations which regularly paid the Sound Due would probably be slightly sympathetic towards the Americans.
As far as the effects of such a war go, things could definately get interesting. Presuming an American victory the Sound Due is abolished for the US, and it seems likely that the US might attempt to acquire the Danish West Indies as well. Presumably the Danish would abolish the Sound Due for the rest of the world shortly after for a lump-sum payment as they did in OTL.
In the US, President Pierce's plummetting reputation might be salvaged by a victorious war against Denmark, and even a modest military buildup could have an effect upon the how much materiel and how many trained men are available at the outbreak of the war (IMO the US Civil War would not be averted by a trade war with Denmark). I am not knowledgeable enough in Danish history to speculate on the effects there, but I would imagine the Danish Navy will be battered and Denmark will be in a weaker position when/if war breaks out with the Germans over Schleswig-Holstein.
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A couple things strike me as interesting here, if matters did come to a Danish-American war.
An American attempt to acquire the Danish West Indies in the 1850s would be politically fraught.
American southern expansionists of an optimistic bent would see this as an opportunity to add a slave territory, if not a slave state.
Antislavery northerners would object to acquiring the islands for the very same reason.
However, the Danes had actually abolished slavery in the islands in 1848. Pessimistic proslavery southerners & racist northerners will not like the prospect of absorbing a free black population into the US. However, anti-slavery northerners would be all the more outraged at the prospect of re-enslaving free blacks.
Over in Europe, it remains an open question how much the US could send to test the sound dues and assert American claims of toll free passage into the Baltic.
However, in 1855, the greatest European powers (Britain, Russia, France) are busy with the Crimean War and in no position to help Denmark even if they wished.
In the meantime, states of the German Confederation have bitter and not too distant memories of the 1848-49 Schleswig war. Prussia in particular, is a non-participant in the Crimean War and might see a chance to get even and take Schleswig-Holstein for itself, or to redeem the Duchies for the German Confederation under another German prince.
Could we see a temporary US-Prussian, US-German Federal coalition vs. Denmark.
I'm not sure how many Danish-Americans there were at the time, I have a vague recollection that the bulk of Scandinavian migration to the US happened later than the 1850s. In any case, German-Americans far outnumber them.
Thoughts?