On November 8, 1861, the USS San Jacinto, commanded by Union Captain Charles Wilkes, intercepted the British Packet_ship mail packet RMS Trent and removed two Confederate diplomats, James Mason and John Slidell. The envoys were bound for Great Britain and France to press the Confederacy’s case for diplomatic recognition by Europe.The initial reaction in the United States was enthusiastically in support of the capture, but many American leaders had doubts as to the wisdom and the legality of the act. In the Confederate States, the hope was that the incident would lead to a permanent rupture in Union-British relations, diplomatic recognition by Britain of the Confederacy, and ultimately, Southern independence. In Great Britain, the public expressed outrage at this apparent insult to their national honour. The British government demanded an apology and the release of the prisoners while it took steps to strengthen its military forces in Canada and in the Atlantic. Several months went by of failed negotiations. This gave Britain the time it required to bring more ships into the Atlantic and adapt them for the warfare they would face. In January 1862, a defamatory letter was sent to the US government. In OTL Prince Albert had got hold of it and edited it before he died. However, the building up of the Navy and preparation for war had meant the letter was postponed. Prince Albert had died in 1861 and the letter got to America unchanged. This was the final straw. The United States formally declared war on the United Kingdom. And so the Fifth Anglo-American War began.
Alliances and Objectives
Britain formed a 'Grand Coalition' of France, Spain, Russia and Prussia to wage war on the USA. The Grand Coalitions objectives were now to render the USA inert and colonise the North American continent. The CSA was recognised by the Grand Coalition but was not part of it.
The US allied itself with Mexico and the United Kingdom of Araucania and Patagonia, whom it offered resources to help it in its independence so they would have another ally against the Grand Coalition.
Under pressure from its principal ally, the UK, the CSA eventually declared war on the Grand Coalition and subsequently collapsed. However, a Confederate general in a last ditch attempt at victory successfully invaded Britain and created the Confederate States of America, Britain and Ireland. In the treaty after the war, the CSA was granted control of a section of American coastline as well as the British Isles though they had to allow immigrants to travel to the new heart of the empire, America.
The War was successful for the Grand Coalition and they each found themselves with new colonial empires.