In 1844, in an accidental explosion that caused many superstitious Americans to believe the office of President had become cursed, John Tyler was killed less than three years after the death of William Henry Harrison due to illness.

President Tyler Killed in AccidentDuring a party aboard the USS Princeton (the first screw stream ship in the Navy), some 400 guests were treated to displays of modern technology, including the 12-inch cannon known as the Peacemaker. It had been fired twice successfully over co-designer John Ericsson's warning that the gun was not ready. The third firing, a tribute as they passed Washington's home at Mount Vernon, caused the cannon to explode. Tyler, who was eager to impress young Julia Gardiner of his virility despite being a 54-year-old widower, had hopped up the ladder onto the deck, just in time to catch shrapnel to his head. Julia's father, New York businessman David Gardiner, and Secretary of State Abel P. Upshur were also among the casualties in the worst peacetime explosion to that point.

Mourning for the disaster included curiosity at another unprecedented occurrence: the ascension of a President pro tempore of the Senate to the office of President of the United States. After the death of Harrison, Tyler had been the first Vice-President to assume the office, though many such as John Quincy Adams and Henry Clay thought that he was meant to fulfill a role rather than be a wholly new president. Despite being nicknamed "His Accidency", Tyler went about resigning from the Whig political party and launching his own economic policy. He vetoed bills for a National Bank repeatedly, causing his cabinet to resign in disgust. While Tyler had a few supporters, such as Daniel Webster, he fought with the Whigs so much that they initiated the first impeachment hearings against him, though it would ultimately be voted down. Tyler's greatest separation from the Whigs, however, was the potential annexation of the Republic of Texas. The matter had been raised before in 1837 with a Texas proposal that was declined by President Martin van Buren. Tyler had Secretary of State Upshur begin work on a treaty, but it remained incomplete at the time of their deaths. What Tyler had planned to be the great issue of the election of 1844 was a political afterthought.

A new story by Jeff ProvineAs President pro tempore of the Senate, North Carolina Whig Willie Person Mangum became the eleventh president of the United States. Mangum was something of a reversal of Tyler, having left the Democratic Party in 1834 after declaring himself a Whig. He left politics and reinvented his career, working as part of a failed Whig plot to nominate four men for president to block out Martin van Buren in 1836 before returning triumphantly to the Senate in 1840. When New Jersey Senator Samuel L. Southard resigned from the Senate in 1842 due to his failing health, Mangum came onto the track that would accidentally make him president. Where Tyler had broken with the Whigs, Mangum worked alongside party leader Henry Clay to institute as much of his American System as possible with the Whig majority in the Senate, though the Democrats controlled the House and resisted several proposed tariffs. A new National Bank was established to capitalize on the rebounding economy after the Panic of 1837, and numerous transportation improvement projects began. These projects would be the main issue of the election of 1844 when Henry Clay narrowly defeated Martin van Buren with the promise of extending the National Road to Oregon and clarifying American control there rather than joint-rule with Britain.

The issue of annexation arose again after the California Republic won its independence from Mexico in 1846 under men such as Mexican general Mariano Guadalupe Vallejo and John C. Fremont. The republic proposed annexation by the United States, but Henry Clay politely declined. Such an annexation might have sparked war with Mexico, who was already upset over American soldiers unofficially participating in the rebellion, seemingly a mirror to Texas. The move is believed to have cost Clay and the Whigs the election of 1848 that gave the White House to Democrat Lewis Cass despite the efforts of the Free Soil Party under Martin van Buren to limit slavery in the territories.

Settlers poured westward on improved roads (including many government-funded rail projects), giving rebirth to the question of slavery in federal territories. Popular sovereignty became the strategy for Kansas and Nebraska Territories, which turned into guerilla warfare as men committed to both sides fought to protect interests. Alongside this issue came the discovery of gold in the newly founded California Republic, which spawned a renewed call for Manifest Destiny. With the approval of Britain, the United States annexed California, prompting Mexico to declare war. The Republic of Texas came as an ally, winning many victories and expanding its territory in the resulting treaty in 1854, which also brought the Republic of Sonora to the US. Some suggested annexing Texas as well, but no formal proposal was made as abolitionists saw it as an extension of slavery and the general attitude of Texas (which had been independent for over a generation) felt best to stay independent.

In 1860, the election of Republican Abraham Lincoln caused the South to declare its independence, inviting Texas to join in a confederation, which it considered before declining and remaining neutral. The war was finished by 1864, and the question of slavery was answered in the United States, though it remained legal in Texas until the 1880s. Texas and the US continued diplomatic relations despite being on opposing sides of the French intervention in Mexico. Suggestions for annexation arose again in the 1890s with a new wave of expansionism, but conservative Texans valued independence while local businesses hoped to hold onto the growing oil industry there. Over the next century, Texans would continue to be friendly with Americans, even joining the Allies in the Second World War, though its production-based economy was especially crippled by the Great Depression. Today it stands as a close trade-partner with the United States, but still fiercely independent.