Bonus Chapter: Some Historical Context for the Story going further
The period of time this story takes place in is loosely based on the period of Italian Unification that occurred between ~1848 and ~1871. Italy was chosen as the setting because the Little Mermaid animated film has been confirmed by Disney as taking place somewhere there. (See 'Fun Facts About Ariel! How Many Do You Know? | Disney Princess' – the Disney Princess YouTube channel).
Italy wasn't always a singular nation: up until the time period aforementioned the peninsula had been a hodgepodge of princely states, religious states, kingdoms and duchies. Among these were the Papal States, the Kingdom of the Two Sicilies, and the Kingdom of Sardinia. The lattermost was arguably the most powerful out of all of them and became the nation which eventually absorbed the others and renamed itself to, 'the Kingdom of Italy'. (This is why Caro asks King Urbino if he doesn't think it's outdated to keep on calling it Sardinia).
The idea of Italian unification didn't come out of nowhere. Many prominent figures of the time were proponents of it, but the two most famous ones are: King Victor Emmanuel II of Sardinia, who eventually became the first King of Italy, and the general Giuseppe Garibaldi, allied with Sardinia, who did the conquering. These two aren't present in the story; King Urbino takes their place as a mixture of both of them. Any actions that this character performs throughout the story are not meant to reflect on the king and general. His personality has also not been based on theirs.
The nation of Calabria is fictionalised, though it is a real region of Italy. The area was in reality part of the Kingdom of the Two Sicilies, which Sardinia took over in 1861. In this timeline, Sardinia under King Urbino has still conquered the Two Sicilies; it just happens that Calabria is its own separate country and was left out of the fray. But like King Urbino says, it is a 'small, remaining nation', which is why at some point he went ahead with renaming Sardinia to the Kingdom of Italy, even without Calabria incorporated.
But this does not mean the king will let it remain as such forever!
A/N: please note that the history displayed here has been heavily condensed and simplified.
