Okay, lets see.
ARW: United States quickly rushes into Halifax and secures Nova Scotia, as well as setting its northern border with Canada at the St. Lawrence river.
1803: Louisiana Purchase (OTL)
1812: United States sits out the Napoleonic war, although the Monroe Doctrine is issued; little is thought of this at the time. Conceding to US demands, the UK agrees to stop supporting Indians against the United States and to end impressment.
1836: Santa Anna, Generalissimo of Mexico, attempts to centralize power--provoking a secession attempt of Texas and a few other Mexican states. Unlike OTL, the United States quickly supports Texas (although not going so far as to declare war against Mexico). This results in a low intensity "Texan War"
1838: Texas is admitted to the United States--the Texan war has become a flashpoint between Mexico and the United States. Mexico breaks all diplomatic ties to the United States. As the conflict continues, the United States begins to mobilze against Mexico.
1839: Second Battle of the Alamo inside Texan territory results in a full scale war against Mexico.
1843: After four years of fighting, the Mexican Government collapses without a peace treaty--and the Mexican State largely dissolves as a result. Successfully in control of most of Mexico, the United States appoints Winfield Scott the first administrator of Mexico. Negotiations will ultimately lead to a much larger annexation than OTL, including all of Baja California, Sonora, and Chihuha, and a large swath of territory further south. Mexico proper is placed under a system of US government administrators until the Mexican Citizenship act of 1868 dissolves the governor system and simply grants US citizenship to former Mexicans.
1857: An Obstinate United Kingdom is finally forced to recognize that they can not hold Oregon Territory against the wishes of its people. Previously demanding the Columbia river as its Southern border, American Immigration into the region simply overwhelmed the numbers of British nationals in the area. By this late point, even Vancouver Island has become mostly American. The US government agrees to pay the United Kingdom a large sum for ending the dispute, and allows the UK to keep Fort Simpson on the Pacific Coast as a major port. Its a rough bargain for the United Kingdom, but at least the United Kingdom gets something for its efforts--questions still remain on whether the UK could have accepted a more moderate offer earlier...
1865: The election of President Abraham Lincoln over political rival Stephen Douglas results in the secession of the Southern United States. Crucially, Virginia declares Neutrality in the conflict while Tenneesse and Kentucky become the major flashpoints for the conflict. Over the course of the war, Lincoln comes to the conclusion that racism, as much as slavery, are the grounds for the conflict.
1871: The US Civil War is over, but the reconstruction is going to have a very different flavor. In order to withdraw federal troops from Mexico, the United States had to grant the rights of citizenship to non-white Mexicans; furthermore, horrific anti-black atrocities are being perpetuated in the defeated Confederate States. It will be a painful road to travel, but reconstruction doesn't simply rebuild the Cotton plantations, it reduces extreme racism from mainstream to a fringe belief. If nothing else, the former Mexicans demand rights as citizens and provide the critical leverage to keep Jim Crow on the sidelines.
1898: Restive Cuba attempts to rebel against its Spanish overlords. This time, the United States decides to act. After a quick campaign, Cuba is made a protectorate of the United States, though with the same rules as the Mexican Act decades before. The Phillipines are allowed to become independent--but this simply means that first Germany and then Japan will take over as colonial overlord.
1915: The April 15th incident triggers what will become a General War in Europe and around the world--except for the United States, which responds by building a navy to safeguard its merchant marine. Abuses by both the UK and Germany leave little desire for the United States to enter this conflict, which results in a German-Austrian-Ottoman Victory at the Expense of Italy, France and Russia. Vladimir Ustinov's Union of Worker's Socialist Republics will emerge as the rise of the Communists, while French "National Actionalism" emerges as a competing right-wing ideology.
1942: World War 2 begins--A Soviet-French-Italian alliance attempts to defeat a moderately democratic Central Europe, while Japan bogs into a decades long war against China. The UK, taking a page from the USA's successes, decides to sit out the war.
1947: World War 2 Ends--Germany and Central Europe are Crushed and partitoned between "Una Europe Allemande" in the West and a "Greater Liberation" in the East, which a border drawn between what used to be Germany. The United States and UK respond by formalizing an alliance to protect themselves from aggression.
1974: World War 3 Begins, as Soviet Chairman Dmitri Bordenko and French President Pierre Laval have lost control over former "Slavonia"
November 14th, 1974: The Day of Disaster. Although eight tactical nuclear weapons have already been deployed in this conflict, the loss of the Ruhr industrial area is something that Actionist France can not accept. Over 1.5 Gigatons of nuclear explosives devastate Europe, as well as China, Japan, India and Baluchistan, which had all taken sides in the conflict.
Although the United Kingdom is not hit by a single nuclear attack, it fares very poorly due to radioactive fallout, which kills as many as 800,000 on the Island in the first year.
All Eyes now turn to the United States, now the largest food producer in the world and entirely undamaged in the conflict. Tens of millions of immigrants flee burning Europe and Asia to seek refuge in the United States. A poisoned United Kingdom enters a special relationship with the United States politically to secure the food they need to avoid widescale famine. A ruined Japan in far worse shape simply begs the United States to be admitted as a territory--largely because the alternative is simply to remain impoverished for at least a century.
1975: The United States is now the most numerous Catholic country in the world. With the full consent of US President Nelson, the Vatican is established in Puerto Rico
2008: Although the United States had originally desired to leave the world well enough alone, it is because of the United States that the world has been able to recover as much as it has from the third world war--and there is the hope that with its active involvement, a fourth war will never happen. With De Facto control over much of Eastern Asia, incorporation of the United Kingdom, Canada, Australia, New Zealand and Iceland into the United States, and nothing less than either puppet regimes or outright territories emerging in devastated Europe, the United States has won the world.