The POD is that Canada chooses to join the American Revolution, instead of remaining part of the British Empire after the United States defeats the British in the American revolution.
1784: The United States of America is formed, following its war of independence with Britain. The States of Maine (Maine encompassing all of OTL New Brunswick), Quebec, Massachusetts, New Hampshire, Vermont, New York, New Jersey, Delaware, Pennsylvania, Maryland, Columbia (North Virginia and South Maryland), Carolina (North and South Carolina combined) and Georgia. As part of the Treaty of Paris, the British agree to cede all of their colonial rule in North and South America. All of the British Caribbean falls under American rule.
1788: The Constitution of the United States is ratified. The State of Quebec is the first state to ratify it, followed shortly by Delaware. Slavery is outlawed in every state. Following filibusters by Georgians and Carolinians in congress, the first amendment is ratified to outlaw the slave trade, and people being born into slavery, but a grandfather clause is included that all current slaves at the time of ratification are still under ownership of their masters until the death of the master (as slaves can no longer be inherited) or the slave.
1797: The United States purchases the Dutch colonies in America.
1800: Following the French Revolution, the new French government decides to cede all of French America to the United States. Haiti, Louisiana, St. Pierre et Miquelon and all of the French Caribbean is ceded to the United States. Guyana is not granted to the United States, and is instead granted independence.
1817: Unprovoked, the United States invades the Spanish American province of Florida. America's occupation of Florida scares Spain so much, they cede both Florida and Cuba to the United States. Spaniards in Spanish America are outraged.
1836: Texas and California secede from Mexico, with California asking to be annexed and Texas, originally wishing to remain independent, eventually favoring annexation by the United States. Russia begins colonization of Alaska.
1847: The United States invades Mexico, with no reason for the invasion other than their wish to expand their country to South America. The Mexican Army is decimated, and the United States continues it expansion to the Central American Union, an independent nation going from Guatemala to Panama under American rule.
1852: Fresh off the war of American Expansion, the US offers to take the Spanish American colonies in the Caribbean and the Gulf of Mexico. Spain refuses, and its American colonies are crushed and annexed by America.
1861: An attempted secession by the southern states (who want the part of the first amendment partially repealed so that slaves can continue to be bought and sold, as almost all of the slaves that were alive in 1788 when the amendment was passed have died) is crushed by President Hannibal Hamlin. He orders Generals Robert E. Lee and and Ulysses S. Grant to put down the rebellion in the Southern States. The rebellion only lasts a few months, and it helps President Hamlin win re-election in 1864, with upstart Illinois politician Abraham Lincoln replacing Andrew Johnson as Hamlin's running mate.
1868: The United States begins colonization of Africa. The Commonwealth of Liberia is formed on the West African coast. It is officially formed as a refuge of the ancestors of black African slaves, if they wish to return to their homeland, but is unofficially a way for "Greater American Republic" to spread their influence in Africa.
1870: The United States invades and conquers Greenland and Iceland. Europe is outraged, and France (who still has incredibly warm relations with the United States) calls it a "great day" in European history.
1872: The United States has gotten so big, that its Congressional legislative branch is replaced with a parliamentary democratic-republic. Now, the President is the head of state and the Prime Minister is the Head of Government (but the President keeps veto power).
1874: The United States buys all portions of German, Belgian and Portuguese Africa from each country. These areas are American Congo (Belgian Congo), New America (OTL Namibia and Angola), American Mozambique (Mozambique), American West Africa (German Kamerun [OTL Cameroon and Niger] and German Togoland [OTL Togo and part of Ghana]), American Burundi and New Canada (Rwanda). These nations would eventually become states of the Union following the African statehood movement.
1877: The Greater American Republic expands to Ecuador, Venezuela and Colombia. Brazil and Argentina unite to "defend" themselves from American Expansionism.
1878: Chile joins Argentina and Brazil. Guyana becomes a US State.
1879: After agreeing in principle to unite against the Ottomans, the Italians, Americans and Germans, the Triple Entente is formed. Other European countries are offered alliance, but only France and the Netherlands show any interest.
1880: The United States assists Irish nationalists in seceding from Britain, pushing the UK and US further apart. American forces guarding the border of American Mozambique along British South Rhodesia are accidentally fired upon by the British. Americans push back strongly, and the United States, and the other Triple Entente nations declare war on the United Kingdom. The war ends quickly, with little fighting, only after Britain - seeing that neither Spain nor France wanted to ally them - agrees to cede all of its African territory to America (small parts going to Italy and Germany), Ireland becomes and independent nation, and Australia and New Zealand are become American states. Britain agrees to everything, only to prevent the German troops from advancing to the English shores.
Part of British Africa going to Italy was British Somaliland, which became united with Italian Somaliland under the the name Free Italian Somaliland.
1881: Pissed-off British subjects are annoyed how their government gave away their entire empire to the United States. A revolt turns into a full blown revolution, removing the monarchy and the elected government with a Fascist nation. The New British Republic trusts no nation, and creates a massive army willing to go to war with any nation that looks at them funny. The leader of the Revolution, Samuel J. Davidson, names himself President for Life of Britain.
1882: British India attempts independence. The Ottoman Empire offers to help the British Army, as does the Empire of Japan. Britain accepts, and the independence movement is swiftly put down. President James G. Blaine of the United States decries it, and decries all British colonialism, saying "Britain's tyranny hasn't earned the right to spread their culture world wide."
1883: Britain invades Ireland under cover of night, and are approaching Dublin by the end dawn. Americans, Italians, Germans, Spanish and France all respond by declaring war on Britain. Britain is invaded simultaneously by Spain and France, with the attempt of removing "Prime Minister" Davidson. Davidson escapes Britain, barely, and Ireland remains independent. Because of the decimation of Britain, all overseas territories become de facto independent. Isle of Britain is divided into the Republics of Scotland, England and Wales, administered jointly by the United States, France and Spain.
1885: The separated Republics on Britain each want to reunite, and a referendum is held in each nation. Each nation overwhelmingly chooses reunification. The Americans, Spanish and French go along with it, but they make sure the first parliamentary elections put the party who they want wins the Prime Ministership.
1892: The Ottomans and Japanese, who now run the puppet states of China and Mongolia, attempt an invasion of India. Japan simultaneously attempts to invade Indochina and the archipelagos the lead off it. Japan succeeds in its invasion of Indochina and the archipelagos, but fails the joint invasion of India.
1895: The Netherlands, Greece and Belgium joins the Triple Entente. Portugal does a few months later.