What if America had been founded as a monarchy, much like Brazil and Mexico, rather than a republic?
The thirteen colonies gain independence from the United Kingdom, and unite into a new state, the American Empire, an absolute monarchy, after the manner of the Roman Empire. George Washington is installed as the first emperor of the new nation, founding the dynasty that would rule for the next three hundred years.
The new Empire quickly becomes good allies with Britain, France, Russia, and Prussia, and begins seeking new lands in the west, with the military aid of the aforementioned European powers. The American-European armies sweep across the west, capturing the Great Lakes region, the Plains, and much of northern Mexico by 1790. The British begin signing away parts of Canada to strengthen their alliance.
America, which by now has already captured all of Mexico north of the Rio Grande, the British-Russian northwest, and eastern Canada, begins expanding north, conquering the last of the unclaimed west within three months, and purchases Alaska from the Russians by the end of the year.
The Empire invades Greenland. Mexico City falls under seige. The new German Empire becomes America's greatest ally, uniting all the German states with the extensive aid of American forces. The new Reich extends from the North Sea to the Mediterranean, and becomes the dominant power in mainland Europe. France and Spain begin to decline, and America and Germany become leading imperial powers, on par with Britain.
America and Germany are major players in the Scramble for Africa, pushing France out as they divide vast areas of the continent between themselves. America takes the west, parts of the Congo, and northern Angola, while Germany takes southern Angola, Namibia, Tanzania, Togoland, Kamerun and Gabon. Over the years, the two nations take all of French and Belgian Africa, deviding it relatively evenly. The rest of the Congo is annexed to Germany, Morocco and Madagascar are taken by America.
The Empire fights on the side of the Central Powers in World War One. America becomes the third party in the new Triple Alliance, and American troupes fight alongside Germans and Turks in most major battles.
America occupies Spain and Portugal, while Germany conquers Belgium, the Netherlands, and Eastern France. The Turks take Greece, Serbia, Romania, and Montenegro, as well as gaining vast amounts of land in Arabia. Britain, Persia, and other regional powers retreat into isolation.
The war ends with the Treaty of Berlin, in which the Western Powers agree to pay for all damage, and cede their colonial possessions. Germany takes British Africa and New Guinea, America takes French Indochina, Australia and Portuguese Mozambique. The Iberian peninsula is placed under German-American co-mandate. The unoccupied region of France is reconstituted as a German puppet state.
Due to American intervention on behalf of the Whites, the Russian Empire never falls, and remains a close American ally. America also aids the Ottomans in crushing the Arab Revolt, securing the entire Arabian peninsula under Turkish rule by 1919.
The French Fascist Party (Francais Parti Fasciste) takes power, establishing the Third French Empire. Under the new regime, France renounces German leadership, and begins a slow process of military rearmament and annexation. France regains much of its eastern land, and incorporates Monaco and Andorra, uniting much of French speaking Europe. With its military power restored, France begins preparations for the invasion of Europe.
French armies invade Spain, wresting the territory from German-American mandate. Germany and America declare war the following day, beginning the Second World War.
Europe separates into two hostile camps: America, Germany and Russia become the Allies, while France, Italy and Britain become the Axis. France conquers Portugal, Belgium, and Alsace-Lorraine, Italy conquers Turkish Albania and Greece, and Britain seizes much of its former African Colonies from Germany. The Allies quickly find themselves on the losing side of the war, and the predicament only worsens when Istanbul falls to the Italians in 1940.
The tables begin to turn with the advent of daylight precision bombing by the Americans. Axis air supremacy is weakened, and Britain's power at sea declines sharply. The two sides are locked in a stalemate for the next year, and the war becomes a quasi-arms race.
The first atom bomb is dropped on Rome. The Italian empire is crushed, and the Axis loses its hold in the Mediterranean region. The Ottoman Empire is liberated and joins the war on the Allies' side, occupying Italy. Subsequent bombings of Paris and London cripple France and Britain.
The Axis surrenders, and Western Europe is freed from the French. Germany is restored to its pre-war borders, Spain and Portugal are reclaimed, and German Africa is returned. Italy's colonies are ceded to America, and the nation comes under Ottoman influence. France is partitioned, with America claiming the west, and Turkey annexing the Mediterranean coast and Corsica. Britain is demilitarized.
The American Empire enters a golden age. Now spanning across all of the Americas, West Africa, Australia, Iceland, Eritrea, Somalia, Djibouti, India, Sri Lanka, Libya, Iberia, New Zealand, Western France and Southeast Asia, it becomes the undisputed world power. Suburbs spread out across the countryside, new innovations explode onto the global market, and desegregation begins.
The social justice movement appears, but never gains much traction. With no Vietnam War, the peace movement never occurs, and public opinion in America remains strongly patriotic. Under the conservative rule of Emperor George VII, American society remains relatively strait-laced and proper. The democrats gain little public support, and become an obscure fringe party.
America conquers Ethiopia, and gains control of the entire Antarctic continent. Japan suppresses a rebellion in Korea with American aid. The tea trade from India becomes the Empire's largest source of income.
A combined force of American, Turkish, and Russian troupes invade Iran, sparking the Iranian War. After three months of continuous invasions on three fronts, Russia lays siege to Tehran, forcing Iran's surrender. The nation is divided in the 1990 Partition Act, with Russia receiving the Black Sea coastal region, Turkey claiming west of the Zagros Mountains, and America taking the rest. The American Empire reaches its height.
The new millennium marks a period of global prosperity. With the modern internet, communication across the Empire improves, allowing the territories to be better administered. The vast nation begins to shrink, as the states and provinces become more interconnected.
Britain rebuilds its alliances and military, and becomes a naval power. Turkey's economy booms, as the spread of automobiles across the third world creates a demand for Arabian oil. With an allied nation dominating the Middle East, Islamic terrorism never becomes a serious threat. The health care system becomes the envy of the world. The job market improves greatly, and the standard of living rises.