The U.S.A. declared its independence from Great Britain in 1776, officially winning their independence in 1783. In 1799-1800, several western and southern states left the Union and won a bloody war of independence, leaving the U.S. with only ten states. Maine later joined as the 11th. Since then, it has taken a largely isolationist attitude, but it has been involved in conflicts like the 2nd American Civil War, the Slave War, World Wars 1 & 2, and the Federate-American War.
As far as modern day global influence goes, it is similar in power to Italy. It does have nuclear weapons, and is fairly innovative when it comes to technology.
American Revolution and Civil War (1776-1802)
The 13 original British colonies declared war on Great Britain in 1776, winning their independence in 1783. They formed the United States of America, writing their constitution and adopting their government in 1787. George Washington was elected as the nation's first president.
Problems arose when President Washington fell terribly ill in 1790. He fought very hard, but died on June 5th. A new president was not chosen until after the funeral, and many debates were held on the powers and role of the new president. Eventually, John Adams was sworn in as the nation's second president.
Events went smoothly until 1794, when the Whiskey Rebellion sprung up in opposition to the unpopular whiskey tax imposed by the federal government. Things became worse when the poorly led force of men that Adams had sent panicked and opened fire at the rebels, killing up to 100 people. This event came to be known as the Whiskey Massacre.
Emotions flared up again in 1799 when revolts sprung up in opposition to war taxes levied by the government. This led to more than a few armed conflicts, and, eventually, calls to leave the Union which the people felt didn't care for their needs. These calls were answered on November 19th, 1799, when several counties in western Pennsylvania agreed to declare independence from the U.S. This was initially regarded as a bit of a joke by government officials, but then Kentucky and Tennessee also declared independence. They were followed by counties in western Virginia (eventually the state of West Virginia) and the states of Georgia, South Carolina, and North Carolina. The Pennsylvania counties formed the state of West Pennsylvania.
These states formed the Confederate States of America and began to fight a bloody war against the U.S. The C.S. gradually lost this war, until the tide of the war was turned when Virginia (and some counties in New York) left the Union and joined the Confederacy. They then began on the path to a fairly quick victory, earning their independence on September 17th, 1802. They also gained all U.S. territory west of the Appalachian Mountains.
Aftermath, The War of 1812, and Onwards (1802-1880)
After the loss in the war, President Adams struggled to keep what was left of the Union together. Several states wanted to become independent themselves, seeing the Union as destroyed already, while several others thought that the entire nation should just join the Confederacy. These factions were eventually convinced that it wouldn't be worth it, though, and the nation continued.
The U.S. and C.S. went to war once again in the War of 1812, when the United States joined the war on Great Britain's side. No territory changed hands in this war.
For the next 60 years, the United States was remarkably stable. Slavery was completely outlawed in the nation in 1845, right after John Quincy Adams' four term presidency. Things remained this way until 1878, when 11 Southern states seceded from the Confederacy. In an unpopular decision, U.S. President William Wheeler decides to bring the U.S. into the war on the Confederacy's side. With most people feeling that the U.S. had no place in this war that didn't concern them, very few people volunteered for the military in those years. The U.S. left the war in 1880, after Samuel J. Tilden was elected president.
Lasting Peace and the World Wars (1880-1945)
The U.S. was then stable again for over 30 years, before they entered World War I in 1917. They barely had time to land troops in Europe before the war was over.
In the mid-1920's, the U.S. and C.S. declared war on the Federated States to force them to end slavery completely. The northern forces won easily, and slavery is ended. The U.S. also gained Puerto Rico.
In the 1930's, the Great Depression happened, and fascist regimes in Germany, Italy, Japan, and the Federated States rose to prominence. This led to World War II, which the Allies won. After the war, the U.S. gained much of Virginia. This territory was incorporated into the state of Maryland. In order to receive the new territory, the U.S. government made Maryland agree to give up all territory on the Delmarva Peninsula to Delaware.
Federate-American War and the 2000's (1945-2010)
In 1970, the Federate States declared war the U.S. in response to the United States allegedly meddling in the F.S.A. presidential elections. The Confederacy did not decide to join this war, so the U.S. went at it alone. This time, after the second deadliest war in history in terms of American casualties, the Federated States came out on top, regaining most of Virginia and a little more. The F.S.A. also gained Puerto Rico. This left Maryland with almost no territory at all, so the U.S. government moderated an agreement between Maryland and Delaware that Maryland could have a strip of land on the Delmarva Peninsula in exchange for Delaware keeping the rest.
Over the next 30 years, the U.S. rebuilt the areas of combat, but otherwise it was peaceful. That leads up to today.
Current Events (2010-present)
Martin O'Malley was inaugurated as the nation's 30th president on January 20th, 2017. He will work with Democratic majorities in both houses of Congress to further Democratic agendas such as universal health care and civil rights for women and homosexuals.
The government of this U.S. is the same as in OTL, except that presidents don't hesitate to run for more than two terms.