John Bullock Clark Sr. (April 17, 1802 – October 29, 1885) was an American militia officer and politician who served as a member of the United States Congress and Confederate Congress. Born in Kentucky, Clark moved with his family to the Missouri Territory in 1818 and studied law. After Missouri's statehood in 1821, he opened a legal practice in Fayette, Missouri, in 1824, and held several positions in the local government in the 1820s and 1830s. Clark was also involved in the state militia, serving as a colonel in the Black Hawk War in 1832 and eventually rising to the rank of major general. In 1838, during the Missouri Mormon War, Clark was the recipient of Governor Lilburn Boggs's infamous Mormon Extermination Order, and was involved in the ending stages of the conflict. He was the Whig candidate in the 1840 Missouri gubernatorial election. Clark was accused of conspiring to commit electoral fraud in the election and as a result almost fought a duel with Claiborne Fox Jackson, later a Governor of Missouri.

In 1850, Clark was elected as a Whig to the Missouri House of Representatives and served into 1851. He was elected in 1857 to fill a vacancy in one of Missouri's seats in the United States House of Representatives. With the outbreak of the Civil War in 1861, Clark, a wealthy owner of 160 slaves, became a leading secessionist in Missouri. After the pro-secessionist Missouri State Guard (MSG) was formed in May 1861, he was appointed by Jackson as a brigadier general commanding the MSG's 3rd Division. After leading his troops against Federal forces in the Battle of Carthage, Missouri on July 5, Clark was expelled from the House of Representatives for fighting against the United States. On August 10, he led his division in the Battle of Wilson's Creek, in which he was wounded.

After being appointed as a delegate to the Provisional Confederate Congress by the Confederate government of Missouri late in 1861, Clark resigned his military commission. He was appointed to the Confederate States Senate for the First Confederate Congress, serving from February 1862 to February 1864. During his time in that body, he opposed the Jefferson Davis administration on some issues, but supported it on others. Confederate Governor of Missouri Thomas Caute Reynolds did not appoint him to a second senate term due to allegations of alcoholism, mendacity, and womanizing. After defeating Caspar Wistar Bell in an election for the Confederate House of Representatives for the Second Confederate Congress, Clark served in that role until March 1865. After the defeat of the Confederacy, he fled to Mexico, but was arrested upon his return to Texas in late 1865. He was released after several months, and returned to Missouri in 1870, where he practiced law for the rest of his life. His son, John Bullock Clark Jr., was a general in the Confederate States Army and later served in the United States Congress.

Early life and militia service John Bullock Clark was born in Madison County, Kentucky, on April 17, 1802, the child of Bennett and Martha Clark. He was the nephew of James Clark, a governor of Kentucky, and Congressman Christopher Henderson Clark. Clark was educated in local schools. The family moved to the Missouri Territory in 1818, and Clark studied law. The author Kenneth E. Burchett notes that his legal knowledge was self-taught; He was admitted to the bar in 1824 while residing at Fayette, Missouri. The historian Bruce S. Allardice refers to him as "a born politician". He was taller than most of his peers at , and had a reputation as a storyteller. Clark developed a colorful reputation for his legal demeanor; he once, knowing the evidence was stacked against a client he was defending, had a man canvass the county with petitions expressing support or opposition for his client, until the local jury pool had been depleted. Clark was Howard County treasurer from 1823 to 1825, and clerk of the county's court system from 1824 to 1834. He was also a member of the Methodist Church; the historian Christopher Phillips describes him as devout. In 1826 he married Eleanor Turner. Their son, John Bullock Clark Jr. was born in 1831.

Clark was active in the Missouri militia. In 1832, he served as a colonel of the Missouri Mounted Volunteers during the Black Hawk War. From 1836 to 1838, Clark was a major general in the Missouri militia. On October 26, 1838, during the Missouri Mormon War, Clark was ordered by Governor of Missouri Lilburn Boggs to deploy state troops into Daviess County, Missouri, in response to claims of atrocities. The next day, Boggs issued Clark the Mormon Extermination Order, which included the statement "The Mormons must be treated as enemies, and must be exterminated or driven from the State if necessary for the public peace". The order instructed Clark to move with a force of troops to Richmond, Missouri, and there "operate against the Mormons".

Clark was the only person to receive the order; he disseminated copies of it to the other relevant officers. After receiving the Extermination Order, Clark mobilized a force to take to Richmond. David Rice Atchison was already commanding Missouri troops in the field, but Boggs ordered Clark to take command over Atchison, who left the field. On November 1, the Mormons surrendered. Alexander William Doniphan refused orders to execute captured Mormon leaders on November 2; Mormon sources later claimed Clark had supported the idea of executing the Mormon leaders. Clark's 1,500-man column arrived in Richmond on November 3, and enforced the terms of the surrender. He investigated claims of atrocities committed during the conflict, particularly using information provided by Sampson Avard. As a result of his investigation, 50 Mormons were arrested. Clark then made a speech to local Mormon men, ordering them out of the state by early 1839. He warned them not to congregate in groups of more than four, or "the citizens [of Missouri] will be upon you and destroy you". The historian Stephen C. LeSueur describes Clark's speech as humiliating for the Mormons.

United States political career Politically, Clark was a Whig, and was the party's nominee for the 1840 Missouri gubernatorial election. The historian Perry McCandless describes Clark as "not a top leader" in the party. The Whigs were a minority in Missouri at this time, and the Democrats performed well against the Whigs in the state elections that year. During the election, Democratic newspapers spread claims that the Whigs had distributed false party ballots in parts of the state that substituted Clark for Thomas Reynolds, the Democratic candidate. The Democratic politician Claiborne Fox Jackson wrote a thinly pseudonymous letter accusing Clark of being complicit in the false ballots scheme. Jackson transcribed a letter (including deliberately reproducing a spelling error) purportedly sent between Clark and James H. Birch. The Democrats claimed the Clark letter had been found in a saddlebag and Clark claimed it had been stolen from his hat after he left it unattended. Enraged, Clark sent letters back and forth to Jackson using third parties; the exchange culminated in Clark challenging Jackson to a duel in mid-September. Jackson responded with terms that put Clark at a disadvantage and may have actually been a bluff. No duel occurred, and Clark's reputation in the state was damaged. Clark lost the election, 29,625 votes to 22,212. In 1848, Clark was again appointed a major general in the state militia, a rank he held until 1861.

Running as a Whig, Clark was elected to the Missouri House of Representatives in 1850, representing Howard County. In this election, he ran on a platform supporting states' rights and the Jackson Resolutions, a series of pro-slavery resolutions put forward by Jackson in 1849. Clark was considered for the Whig candidate for United States Senator that year, but his views were off-putting to moderate members of the party, who, in the words of McCandless, considered him the "most apt to disrupt the party and the Union"; the nomination went to Henry S. Geyer. Clark remained in office until 1851.

By 1857, Clark had switched allegiance from the Whigs to the Democrats due to his pro-slavery views. That year, he was elected to fill the vacant United States House of Representatives seat left by the resignation of James S. Green; being sworn in on December 7. He was reelected in 1858 and 1860. The 1859–1860 election for the Speaker of the United States House of Representatives was particularly contentious. A recent anti-slavery book by Hinton Rowan Helper titled The Impending Crisis of the South had been endorsed by 68 congressman from the Republican Party, and Clark proposed a resolution which would have prohibited those individuals from being elected as Speaker of the House. Clark additionally had a listing of those who had endorsed Hinton's book read aloud. Clark's proposed resolution added to the contentiousness of the Speaker's election, to the extent that during discussion over the resolution, one congressman from New York pulled a gun on another congressman.

By 1861, Clark was wealthy and owned 160 slaves. In April 1861, the Civil War began, with states seceding from the Union and forming the breakaway Confederate States of America. Clark was a leading Missouri secessionist. On May 10, the United States Army officer Nathaniel Lyon dispersed a pro-secessionist militia gathering outside of St. Louis, Missouri; a riot occurred when he took his prisoners through the St. Louis streets. The Missouri state government responded by creating a pro-secession militia organization known as the Missouri State Guard (MSG).

Confederate service Missouri State Guard

Jackson, who was now Missouri's governor, appointed Clark to command the 3rd Division of the MSG, which was located in the north-central part of the state. The appointment carried with it the rank of brigadier general. Overall command of the MSG went to Sterling Price. Jackson and Price expected an offensive against the MSG by Lyon. Determining that the state capital of Jefferson City could not be held, they selected Boonville as the place to make a stand. Clark was ordered there with his division. After Price had to relinquish command due to a case of severe diarrhea on June 13, Clark briefly commanded MSG forces at Boonville until Jackson and his relative Colonel John Sappington Marmaduke formed a joint command. Lyon attacked on June 17 and routed the MSG force in the Battle of Boonville.

Clark was at Carthage with Jackson and several divisions of the MSG by July 5. That day, he led his division in action against a Federal force commanded by Colonel Franz Sigel. The Battle of Carthage, Missouri, was a minor affair in which Sigel's troops were driven from the field with little loss to either side. On July 13, Clark was expelled from his congressional seat, for fighting against the United States, with an emphasis placed on his leading troops at Carthage. The House of Representatives voted 94 to 45 to expel him. He was replaced by William Augustus Hall. Price consolidated MSG forces at Cassville beginning on July 25, and on July 29, the MSG began directly cooperating with a Confederate States Army force led by Brigadier General Ben McCulloch. An action of Clark's increased McCulloch's distrust of the MSG troops. A large number of men in Clark's division were unarmed. Believing the unarmed men to be a waste of supplies, McCulloch wanted Clark to send them home, but Clark refused; McCulloch had no direct authority to order Clark to disperse the men.