Bellum Britannica

Hello! This alternate history will show a world in which Great Britain goes to war with the United States in 1861 as a result of the Trent affair. Who would win, and what would be the result? Let's find out!
== World War One (American Theatre) ==
We begin in 1861. The American Civil War began on April 12, 1861. P.G.T. Beauregard, commander-in-chief of the new Confederate Army, captured Fort Sumter from Major Robert Anderson's 77-man garrison.
The Confederate States of America was established on February 8, 1861. The states of South Carolina, Mississippi, Florida, Louisiana, Alabama, Georgia, and Texas secede, made the Confederacy, and put the capital at Montgomery, Alabama. Jefferson Davis was the president. 
The United States President, Abraham Lincoln, at first did not seem to mind. But when Sumter fell, it all changed. He called for 75,000 militia to serve for three months and crush the rebellion.
In response, Virginia, North Carolina, and Arkansas seceded. Tennessee, while not outright seceding, made an alliance with the Confederacy and contributed troops to both causes.
The first Union invasion began on July 8. The Confederates were taken completely by surprise. They fell back to Fredericksburg.
Lincoln called for a blockade of the Confederacy. Great Britain and France did not like this. Then came the kicker.
On November 8, 1861, the RMS Trent was apprehended by a Union ship, the USS San Jacinto. On November 30, the British sent an angry reply. On December 27, the United States declared war.
In response, France declared war on the United States on January 1, 1862. The Civil War had gone from a local war to a world war in a matter of days. It promised to be long and bloody.
Meanwhile, McDowell had been given George B. McClellan as chief-of-staff. They immediately began to prepare for an invasion. Thousands of recruits came in, all to be trained. McClellan was am aster organizer and trainer, while McDowell was an excellent military leader.
The Confederates had been driven out of Missouri by September. Brigadier-General Ulysses S. Grant took 3,000 men to Belmont. There, the biggest Union disaster of the war happened, though no one realized that it was anything more than a minor defeat at the time.
Leonidas Polk commanded 5,000 men. They were driven out of Belmont, but recaptured the camp in a vicious battle. Grant was killed, and Polk moved north.
Vengeance seethed through the Confederate forces. Polk moved north, taking Cairo. Illinois militia came in to stop him, but Polk's veterans drove them off. 
Albert Sidney Johnston took advantage of the situation. He drove north, defeating a small Union force under Don Carlos Buell. The Midwest was soon under Confederate control.
Johnston had begun his drive north on December 2, 1861. Illinois and Missouri were abandoned by the North. The Union forces fell back. After the Battle of Youngstown, Ohio was in Southern hands.
Michigan, Indiana, and Illinois fell. Pittsburgh fell. The United States was certainly going to lose. 
In Virginia, 10,000 Frenchmen bolstered the Army of Northern Virginia. They went on the offensive on February 24, 1862. The Union forces fell back to Washington.
Lincoln created two armies to invade Canada with. 116,000 men were involved. One was under John Pope, and the other under Henry W. Halleck.
Halleck moved forward with the 65,000-man Army of the Niagara. He seized Toronto. The British fought a heroic delaying action at almost every town.
Pope, with the 51,000-man Army of the Hudson, moved north. He seized Montreal in a big battle on May 10, then wanted to link with Halleck. But Halleck was still fighting in southern Ontario.
Pope moved up to Quebec. He only had 31,000 men now against the 55,000 British and more Canadian militia. The British had more men coming in.
The British were commanded by Lieutenant-General Sir William Fenwick Williams. Pope launched a big frontal attack on July 19. The British regulars did a number on the Americans.
Pope had to fall back after the Battle of the Plains of Abraham. He and Rosecrans stayed in Canada, living off the land. Pope's policies, however, created a tense situation. Canadian militia created chaos in the rear.
At sea, the United States Navy was wiped out. It only had 264 ships at the beginning of 1862, to Great Britain's 339. France had another 220 ships, and the Confederacy had approximately 94. The Union blockade was over, and the Confederacy was able to make a fleet of ironclads. 
On April 13, at the Second Battle of Hampton Roads, a Confederate ironclad fleet battled it out with a Union ironclad fleet. It was inconclusive, but it was made by the press to look really important.
The British had landed on the California coast on April 6, taking control of San Francisco. They moved inland with 10,000 Indian troops. 
The United States could not win. Russia had joined the war, and the fighting would continue in Europe. World War One had begun. However, the United States surrendered on August 1, 1862. 
== World War One (European Theatre) ==
In Europe, meanwhile, Russia had joined the war on the side of the United States. The new German Empire had joined it, along with Italy. Austria, Denmark, and Turkey had joined Great Britain and France.
German forces moved into Denmark swiftly. The Danes scored a few victories, but they could not resist long. They were invaded on April 1. Denmark surrendered on November 29.
They then turned onto Austria. They assumed that France would be the hardest enemy, and that it would take the longest to mobilize. So they wanted to defeat their other enemies first.
Austria had opposing armies coming in from all sides. 437,000 Germans, 200,000 Italians, and 232,000 Russians attacked. Austria surrendered on March 30, 1863, after exactly four weeks.
France, by now, had 910,000 men. Germany deployed 940,000 men to invade France. The biggest invasion of the war began on August 6, 1863.
France had help. 44,000 British troops were stationed on the northern flank of the Allied armies. They were the British Expeditionary Force B. British Expeditionary Force A was on its way from Canada.
Germany struck on August 6. It was hard fighting. However, the Germans had advanced as far as Sedan by September 1. There, in a hard fight, German forces, numbering 250,000, were defeated by French and British forces numbering 164,000.
The Allied forces had a major breakthrough. French forces moved to retake Metz. However, once the Siege of Metz was lifted, the Allies could not do much more. The war was a stalemate.
On April 14, 1865, Germany, Great Britain, France, Russia, and Italy agreed to an armistice. Turkey had surrendered to Russia. The armistice agreed that the borders would be where the battle lines stood.