First use of general anesthesia in an operation, by Crawford Long.
The first electrical telegraph sent by Samuel Morse on May 24, 1844 from Baltimore to Washington, D.C..
On August 29, 1842, the first of two Opium Wars ended between China and Britain with the Treaty of Nanking. One of the consequences was the cession of parts of modern day Hong Kong to the British. Hong Kong would eventually be returned to China in 1997.
Mexican-American War (1846 - 1848) was fought between Mexico and the United States of America. The latter emerged victorious and gained undisputed control over Texas while annexing portions of Arizona, California and New Mexico.
Wave of revolutions in Europe. Collectively known as the Revolution of 1848. This led to mass emigration of these refugees into industrial cities of the United States as well as to other locations around the world.
Karl Marx and Friedrich Engels writes The Communist Manifesto, first published on February 21, 1848.
In the midst of the Second Great Awakening, preacher William Miller predicts the Second Advent of Jesus Christ will occur on October 22, 1844. Christ's failure to appear became known as the Great Disappointment.
In the mid 1840s several harvests failed across Europe, which caused famines. Especially the Great Irish Famine (1845-1849) was severe and caused a quarter of Ireland's population to die or emigrate to the United States and Canada.
Introduction of the postage stamp. The first of them is Penny Black, issued by the United Kingdom on May 1, 1840.
President Martin Van Buren (United States)
President William Henry Harrison (United States)
President John Tyler (United States)
President James Knox Polk (United States)
President Zachary Taylor (United States)
President Sam Houston (Republic of Texas)
President Anson Jones (Republic of Texas)
So, we've got the Opium Wars, Texas wasn't a state but a Republic with it's own president, the Great Irish Potato Famine & the mass migration of Irish to the US, the birth of Communism.............you actually have a lot to work with here.