Missouri is a state located in the Midwestern region of the United States of America. It is bordered by eight states: Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. Missouri was originally purchased from France as part of the Louisiana Purchase. The Missouri Territory was admitted into the union as the 24th state in 1821. The state has 114 counties and one independent city.

St. Louis, the largest metroplitan area in Missouri is known as the "Gateway to the West" because it served as a departure point for settlers heading to the west as well as the starting point and the return destination of the Lewis and Clark Expedition. It is a state with both Midwestern and Southern cultural influences, reflecting its history as a border state between the two regions. The state is named after the Missouri Siouan Indian tribe whose Illinois name, ouemessourita (wimihsoorita), meaning "those who have dugout canoes." The confluence of the Mississippi and Missouri rivers is located in Missouri.

Originally part of the 1803 Louisiana Purchase, Missouri was admitted as a state in 1821 as part of the Missouri Compromise. Originally the state's western border was a straight line, defined as the meridian passing through the Kawsmouth, the point where the Kansas River enters the Missouri River. The river has moved since this designation. This line is known as the Osage Boundary. In 1835 the Platte Purchase was added to the northwest corner of the state after purchasing the land from the native tribes, making the Missouri River the border north of the Kansas River. This addition made what was already the largest state in the Union at the time (about 66,500 square miles to Virginia's 65,000 square miles (which included West Virginia at the time) even larger.

Many of the early settlers in western Missouri came from the southern states, and along with them came the institution of slavery. In the area of Independence and areas just north of there, Mormon settlers began arriving in the early 1830s. It wasn't long before conflict arose between the "old settlers" (mainly from the south originally) and the Mormons (mainly from the north and Canada). The "Mormon War" erupted and by 1839 the Mormons had been expelled from Missouri. In 1838-1839 a border dispute with Iowa over the so-called Honey Lands resulted in both states calling up militias along the border.

After many incidences with Kansans crossing the Western border (including a fire in the historic Westport area of Kansas City), a border war began between Missouri and Kansas. The tradition continues between the University of Missouri - Columbia and University of Kansas. The rivalry is mainly focused on football between the two colleges. It is the oldest college rivalry west of the Mississippi River and the second oldest in the nation. Each year when the universities meet to play, the game is coined "Border Showdown." An exchange occurs following the game where the winner gets to take a historic marching band drum which has been passed back and forth for decades.

After the secession of Southern states began, the Missouri legislature called for the election of its own special convention on secession. The convention voted decisively to remain within the Union, but pro-Southern Governor Claiborne F. Jackson ordered the mobilization of several hundred members of the state militia who had gathered in a camp in St. Louis for training. Union General Nathaniel Lyon struck first, encircling the peaceful camp and forcing the state troops to surrender. Lyon then directed his soldiers, largely non-English-speaking German immigrants, marched the prisoners through the streets then opened fire on the largely hostile crowds of civilians who gathered around them, killing unarmed prisoners as well as men, women and children of St. Louis in an incident that became known as the "St. Louis Massacre."

These events caused greater Confederate support within the state. Governor Jackson appointed Sterling Price, president of the convention on secession, as head of the new Missouri State Guard. Jackson and Price were forced to flee the state capital of Jefferson City on June 14, 1861, in the face of Lyon's rapid advance against the state government. In the town of Neosho, Missouri, Jackson called the state legislature into session where they enacted a secession ordinance that was recognized by the Confederacy on October 30, 1861. With the elected governor absent from his capital and the legislators largely dispersed, Union forces installed an unelected pro-Union provisional government with Hamilton Gamble as provisional governor. President Lincoln's Administration immediately recognized Gamble's government as the legal government, which provided both pro-Union militia forces for service within the state and volunteer regiments for the Union Army.

Fighting ensued between Union forces and a combined army of General Price's Missouri State Guard and Confederate troops from Arkansas and Texas under General Ben McCulloch. After winning victories at the battle of Wilson's Creek and the siege of Lexington, Missouri and losses elsewhere, the Confederate forces had little choice but to retreat to Arkansas and later Marshall, Texas, in the face of a largely reinforced Union Army. Though regular Confederate troops staged large-scale raids into Missouri, the fighting in the state for the next three years consisted mainly of guerrilla warfare conducted by citizen soldiers such as Colonel William Quantrill, Frank and Jesse James, the Younger brothers, and William T. Anderson. Such small unit tactics pioneered by the Missouri Partisan Rangers were also seen elsewhere in occupied portions of the Confederacy during and after the Civil War.

In 1865, Missouri abolished slavery, doing so before the adoption of the Thirteenth Amendment to the United States Constitution by an ordinance of immediate emancipation. Missouri adopted a new constitution, one that denied voting rights and had prohibitions against certain occupations for former Confederacy supporters.

The Missouri's Women's Suffrage Club was organized in 1867, to win the right to vote for women, and was the first such club in the nation. Missouri adopted its 3rd constitution on October 30, 1875. In 1882, the bank robber Jesse James was killed in Saint Joseph.

On March 1, 1912, US Army Captain Albert Berry made the first parachute jump from a moving airplane over Missouri. In 1919, Missouri became the 11th state to ratify the 19th amendment, which granted women the right to vote.

The first president from Missouri, Harry S. Truman, assumed the presidency in 1945 after the death of Franklin D. Roosevelt. Truman was re-elected in 1948. Construction began on the Saint Louis Gateway Arch in 1965. In 1980, court-ordered desegregation began in Missouri.