Disclaimer: I do not own Frozen, they belong to Disney.
Prologue
No one saw it coming. Not the Queen, not her advisors, not the Princess, not the Captain of the Guard, no one.
Yet there they were, stationed just at the opening of the fjord, as tangible as the mountains under the afternoon sun. The proud battleships stood tall and shoulder to shoulder, acting as a barricade and prohibited any escape. The flag of the Southern Isles could be seen on every mast as it flapped against the strong winds.
A messenger came later in the evening, carrying a letter from the youngest Prince of the Southern Isles; Prince Hans. To say that the Queen was shocked would have been deeply under-exaggerated, seeing that she nearly froze everyone and everything within the room they occupied once the messenger announced the name. In the message, it gave a warning. Stating that if Arendelle did not surrender, it would be a declaration of war and the Southern Isles will attack.
Almost immediately after the letter was read, there was uproar, courtesy to the Princess, who reacted in the most aggressive, yet understandable way: by throwing a chair across the room and shouting at the top of her lungs the disbelief she felt. Had it not been for Arendelle's Ice Master and Deliverer, the Princess would have lunged at the messenger. The advisors shared the Princess's livid emotions, saying that what the letter was complete and utter nonsense, and argued that it was the Southern Isles that declared war once they entered the threshold of the fjord with their battleships. The messenger, on his part, simply argued that he was following his orders and awaited their response, if no response was given, the Southern Isles would attack anyways.
The Queen stood regal and silent as the bickering took place and only when all heads turned to her did she give the final response: Arendelle would not surrender.
At first thought, one would say that her choice was foolish. Arendelle's navy was strong, but when compared to the one they saw in front of them, it was obvious that the scales were tipped a bit towards the Southern Isles. But the Queen knew that if she were to just surrender her kingdom, her citizens will never forgive her. Yes, she might be saving countless lives by surrendering, but who is to say that they will be treated fairly and justly after the surrender? Who is to say that they will not be prosecuted and miserable?
When the Queen made her decision, it was not to save face. No, she made that decision because she knew that her citizens would rather die than surrender to a nation as despicable as the Southern Isles.
And thus, Arendelle readied her ships, capable men volunteered and the rest, such as women and children, were taken to a safe location.
The Battle of Arendelle had begun.