The Empire of New Jersey timeline is one in which New Jersey seceded from the Union during the First World War, although the POD dates to the American Civil War and various sour grapes. The Empire was originally the Free and Independent State of New Jersey, or alternately the Garden Empire.
New Jersey's contempt for Abraham Lincoln is greater than in OTL, and people not only reject Lincoln twice in elections, they take to the streets about it. The Independence Movement is born and simmers over the next few decades. Woodrow Wilson took over the movement in 1905, and he uses discontent over the tensions surrounding WWI to secede from the Union, along with other states, during the Great Secession.
In 1916, the Black Tom Explosion rocks the harbor of Jersey City, wrecks Ellis Island and the Statue of Liberty, and creates much damage to Jersey City, sparked by German saboteurs. At the same time, Germany encourages Mexico to attack the United States and the Southern establishment to secede from the United States. Several states, including Mississippi, Texas, Alabama, Georgia, New Mexico, and both Carolinas take Mexico up on the offer, and spies infiltrate Sacramento, telling California to do the same. New England revives sour grapes from the previous century (including complaints about Southern dominance from the early 19th century), and secedes as a group. New York is torn in dispute. The city of New York (and New Jersey) want to fight the Germans, but upstate New York is convinced that the Black Tom disaster was an accident, and the federal government in Washington agrees with the upstaters. Upset about the war, New Jersey and New York City secede from the USA and set up the "Free and Independent State of New Jersey". Philadelphia joins the Free and Independent State in 1917, and northern Delaware in 1918. The United States fragments further, and by the mid-1920s is largely restricted to the Midwest, having abandoned Washington in favor of Chicago.
Germany wins the war in mainland Europe (setting up puppet states in Poland, the Ukraine, and Belarus, annexing Austria, and keeping Alsace-Lorraine). Russia has the Russian Revolution. The British Empire stays intact and still gains Palestine, although France doesn't take Syria.
Nonetheless, New Jersey, although on the losing side of the war on the Continent, manages to gain a seat at the negotiations table in Versailles, and gains "mandatory" territory in areas taken over from the Ottoman Empire (including the southern Palestinian port of Eilat) and the Netherlands (in the East Indies). New Jersey continues to industrialize, with plants in Trenton, Newark, and Camden cranking out ships, troops, and munitions. The Free State rapidly gains an army and a navy, as well as an air corps. It still does not have all that much land.
With plenty of Jews on the Free State's soil, New Jersey keeps its borders open to Jewish immigrants. Furthermore, because Germany won, there's no "stab-in-the-back myth" to encourage failed painters such as Adolf Hitler. He remains an unknown. The Holocaust doesn't happen in the Free State's timeline. Other genocides do, however, such as the Holodomor under Josef Stalin and a later Soviet genocide against Jews. Those genocides lead to further waves of refugees.
In the late 1920s and early 1930s, the Free State starts expanding in an effort to gain a hinterland. Long Island, much of lower upstate New York, Eastern Pennsylvania, the remnants of Delaware, and much of Maryland are overrun. The Free State keeps its capital at Trenton, though.
The 1940s are largely uneventful, but WWII breaks out in the early to mid 1950s, with the main factions being the British- and German-dominated capitalists and the Russian-dominated communists. Japan comes into play mid-war, first aiding the communists and then switching to the capitalists, as Hirohito (the Showa Emperor) decides the capitalists make a better gamble. New Jersey largely stays out of this conflict, except to supply arms. It remains a flourishing democracy up until the late 1960s.
Fred Trump grows in power, aided by his right-hand man Robert Moses), in the late 1960s, and amasses enough military support for a coup in 1969, ruling at the head of a military junta. In 1970, he proclaims himself the first Emperor of New Jersey, Frederick the 1st, with his successor being Prince Frederick the 2nd. Newspapers initially make fun of this proclamation, only to get quickly shut down and their offices burned. The New York Daily News and New York Post both get dynamited, and the New York Times' staff only manage to save their publication by sneaking away to Boston. The Imperial Star-Ledger is named the official newspaper of the Empire, as well as the Trenton Times. An Imperial media facility is established as well. The Emperor names Prince Donald the "Grand Architect of Trenton", and plans are set about to turn grimy industrial Trenton, the capital, into a grand Imperial City worthy of an Empire. Mass demolitions take place in downtown Trenton and along the Delaware River.
The Empire of New Jersey sets about improving its military and sending out troops and ships to gain new areas. Jerusalem falls to the New Jerseyans in 1972, ending a quiet ownership by local Palestinians (who had taken it over from the British). Jews see this as an opportunity for settlement, and a surge of migration overseas occurs to the Holy City. Jakarta falls in 1975, and the Empire annexes the Republic of Albany in 1977. It threatens the Republic of New England, and tensions build through the late 1970s and early 1980s. The Empire explodes its first nuclear weapon in upstate New York in 1981, and it soon amasses a nuclear stockpile. In 1988, New Jersey gains Singapore. Crafty Prince Donald massacres his siblings shortly after his father dies in 1995, becoming Emperor Donald the 1st. Donald quickly moves to cut off immigration to the Empire and tries to impose segregationist measures (against black people and Asians), a move which backfires because of the very diversity of the Empire's population. A recession hits in the early 2000s, causing discontent to grow.
Riots break out, leading to greater and greater campaigns of suppression. Camden is devastated by a riot in 2003, Newark in 2004, New York City in 2005. Philadelphia suffers massive fires later that year, and the rebels start organizing in the Pine Barrens and other hideaways. Atlantic City, a seedy seaside resort, and Wildwood, another somewhat seedy seaside resort, become centers of the Resistance, and soon this Resistance militarizes and threatens civil war. Revolutionaries march on Trenton, and street battles break out. Atrocities lead to fires all over Trenton, and finally Donald has to flee the country. He flies down to Florida, which grants him amnesty.
New Jersey's revolutionaries march to Princeton to proclaim a new constitution at Nassau Hall, on the Princeton University campus, and also to Old Queens, in New Brunswick - Rutgers University's campus. Their declaration asserts that Liberty and Prosperity shall once again reign over the State of New Jersey. However, even as a republic, the people decide to keep the name "Empire". Colonial delegations from the Indies and from Palestine show up, objecting to that title, but are overruled by the "homelanders". A President of New Jersey, Alice Rabinowitz, is elected, the first Jew to be a national leader, as well as the first woman. She has a term of five years, and is reelected for a second term in 2010. She is succeeded by more traditionalist Christopher Christie in 2015, who is president for a term, followed in 2020 by Stephen Sweeney.
The Taylor company marketed "Taylor ham" in the northern parts of New Jersey, a name which carried over to the northern parts of the Free State, and later the Empire. People in the center and south referred to the same dish - slices of pork with cheese on a bagel - as "pork rolls". Well, this argument carried over to the colonies. Singapore refers to the dish as Taylor ham, the East Indies territories call the meal a pork roll, and the Palestinian folks call it "trayf" (non-kosher) or "haram" (non-halal), depending on whether they're Jewish or Muslim.