Question: Who wrote a letter to Orville Browning where he recognized the importance of one of the four slave states that never declared a secession in the Civil War?

full_context: Document 1: Benjamin Hardin Helm: Benjamin Hardin Helm (June 2, 1831 – September 21, 1863) was a Kentucky politician, attorney, Confederate brigadier general, and a brother-in-law of Abraham Lincoln. He was also the son of Kentucky Governor John L. Helm. Helm was born in Bardstown, Kentucky. He attended the Kentucky Military Institute and the West Point Military Academy and then went to study law at the University of Louisville and Harvard University. He served as a state legislator and the state's attorney in Kentucky. He also served as the assistant inspector-general for the Kentucky state guard. Helm was offered the position of Union Army paymaster by his brother-in-law, President Abraham Lincoln, a position which he declined. Helm felt it was an honor to serve in the Confederate States Army, where he was initially a colonel and later promoted to brigadier general. Helm commanded the 1st Kentucky Brigade more commonly known as The Orphan Brigade. He died on the battlefield during the Battle of Chickamauga. Helm was married to Emilie Todd, the half-sister of Mary Todd Lincoln.
Document 2: Slave states and free states: In the history of the United States of America, a slave state was a U.S. state in which the practice of slavery was legal, and a free state was one in which slavery was prohibited or being legally phased out. Historically, all the British colonies had practiced slavery. The division between slave and free states began during the American Revolution (1775–1783). Slavery became a divisive issue and was the primary cause of the American Civil War. The Thirteenth Amendment to the United States Constitution, ratified in 1865, abolished slavery throughout the United States, and the distinction between free and slave states ended.
Document 3: Indianapolis in the American Civil War: During the American Civil War, Indianapolis, the state capital of Indiana, was a major base of support for the Union. Governor Oliver P. Morton, a major supporter of President Abraham Lincoln, quickly made Indianapolis a gathering place to organize and train troops for the Union army. The city became a major railroad hub for troop transport to Confederate lands, and therefore had military importance. Twenty-four military camps were established in the vicinity of Indianapolis. Camp Morton, the initial mustering ground to organize and train the state's Union volunteers in 1861, was designated as a major prisoner-of-war camp for captured Confederate soldiers in 1862. In addition to military camps, a state-owned arsenal was established in the city in 1861, and a federal arsenal in 1862. A Soldiers' Home and a Ladies' Home were established in Indianapolis to house and feed Union soldiers and their families as they passed through the city. Indianapolis residents also supported the Union cause by providing soldiers with food, clothing, equipment, and supplies, despite rising prices and wartime hardships, such as food and clothing shortages. Local doctors aided the sick, some area women provided nursing care, and Indianapolis City Hospital tended to wounded soldiers. Indianapolis sent an estimated 4,000 men into military service; an estimated 700 died during the war. Indianapolis's Crown Hill National Cemetery was established as one of two national military cemeteries established in Indiana in 1866.
Document 4: Outline of the American Civil War: American Civil War – civil war in the United States of America that lasted from 1861 to 1865. Eleven Southern slave states declared their secession from the United States and formed the Confederate States of America, also known as "the Confederacy." Led by Jefferson Davis, the Confederacy fought against the United States (the Union), which was supported by all the free states (where slavery had been abolished) and by five slave states that became known as the border states.
Document 5: Kentucky in the American Civil War: Kentucky was a border state of key importance in the American Civil War. President Abraham Lincoln recognized the importance of the Commonwealth when, in a September 1861 letter to Orville Browning, he wrote:
Document 6: American Civil War: The American Civil War (commonly known as the "Civil War" in the United States) was fought in the United States from 1861 to 1865. The result of a long-standing controversy over slavery, war broke out in April 1861, when Confederates attacked Fort Sumter in South Carolina, shortly after Abraham Lincoln was inaugurated. The nationalists of the Union proclaimed loyalty to the U.S. Constitution. They faced secessionists of the Confederate States of America, who advocated for states’ rights to perpetual slavery and its expansion in the Americas.
Document 7: Confederate government of Kentucky: The Confederate government of Kentucky was a shadow government established for the Commonwealth of Kentucky by a self-constituted group of Confederate sympathizers during the American Civil War. The shadow government never replaced the elected government in Frankfort, which had strong Union sympathies. Neither was it able to gain the whole support of Kentucky's citizens; its jurisdiction extended only as far as Confederate battle lines in the Commonwealth. Nevertheless, the provisional government was recognized by the Confederate States of America, and Kentucky was admitted to the Confederacy on December 10, 1861. Kentucky was represented by the central star on the Confederate battle flag.
Document 8: President Lincoln's 75,000 volunteers: On April 15, 1861, at the start of the American Civil War, the President of the United States, Abraham Lincoln, called for a 75,000-man militia to serve for three months following the bombardment and surrender of Fort Sumter. Some slave states refused to send troops against their neighboring slave states, with the result that most such states also declared secession from the United States and joined the Confederate States.
Document 9: King Cotton: "King Cotton" as a slogan summarized the strategy used before the American Civil War of 1861–1865 by pro-secessionists in the Southern States (the future Confederacy) to claim the feasibility of secession and to prove there was no need to fear a war with the Northern States. The theory held that control over cotton exports would make a proposed independent Confederacy economically prosperous, would ruin the textile industry of New England, and—most importantly—would force Great Britain and perhaps France to support the Confederacy militarily because their industrial economies depended on Southern cotton. The slogan, widely believed throughout the South, helped in mobilizing support for secession: by February 1861, the seven states whose economies were based on cotton plantations had all seceded and formed the Confederacy (C.S.A.). Meanwhile, the other eight slave states, with little or no cotton production, remained in the Union.
Document 10: Kentucky: Kentucky ( , ), officially the Commonwealth of Kentucky, is a state located in the east south-central region of the United States. Although styled as the "State of Kentucky" in the law creating it, Kentucky is one of four U.S. states constituted as a commonwealth (the others being Virginia, Pennsylvania, and Massachusetts). Originally a part of Virginia, in 1792 Kentucky became the 15th state to join the Union. Kentucky is the 37th most extensive and the 26th most populous of the 50 United States.
Document 11: Barnesville's Post: Barnesville's Post located near Barnesville, in Bourbon County, Kansas, was the site of military camps for stretches of time during the American Civil War. The first mention of a camp there came from a report written on September 4, 1861, by Sen. James Lane. This was during the time Lane had evacuated Fort Scott and moved his forces to areas north of that post. A post was established at Barnesville. Lane wrote to Capt. W. E. Prince, then commanding Fort Leavenworth, "I am holding Barnesville . . . with an irregular force of about 250 men, stationed in log buildings, and am now strengthening their position with earth entrenchments."
Document 12: Border states (American Civil War): In the context of the American Civil War (1861–1865), the border states were slave states that did not declare a secession from the Union and did not join the Confederacy. To their north they bordered free states of the Union and to their south they bordered Confederate slave states. Of the 34 U.S. states in 1861, nineteen were free states and fifteen were slave states. Four slave states never declared a secession: Delaware, Kentucky, Maryland, and Missouri. Four others did not declare secession until after the Battle of Fort Sumter and were briefly considered to be border states: Arkansas, North Carolina, Tennessee, and Virginia—after this, they were less frequently called “border states”. Also included as a border state during the war is West Virginia, which was formed from 50 counties of Virginia and became a new state in the Union in 1863.
Document 13: Kentucky Vehicle Enforcement: The Kentucky State Police Division of Commercial Vehicle Enforcement (CVE), commonly known in the Commonwealth as "Kentucky Vehicle Enforcement" (KVE), is a statewide law enforcement agency for the Commonwealth of Kentucky. The department, which was a stand-alone department until July 14, 2008 executive order from then-Governor Steve Beshear, is now a division of the Kentucky State Police (KSP). The division employs both sworn officers and civilian commercial vehicle inspectors. CVE's primary mission is the enforcement of all state laws/regulations on commercial and non commercial vehicles traveling throughout the Commonwealth of Kentucky. CVE's secondary mission is to conduct drug interdiction operations on the Commonwealth's state and county highways, working jointly with the KSP's Special Operations Division D.E.S.I. (Drug Enforcement and Special Investigations) unit. The CVE division operates and monitors the Commonwealth's system of commercial vehicle weigh stations throughout Kentucky. Their headquarters is located in Frankfort.
Document 14: Florida in the American Civil War: Florida joined the Confederate States of America at the beginning of the Civil War, as third of the original seven states to secede from the Union, following Lincoln's 1860 election. With the smallest population, nearly half of them slaves, Florida could only send 15,000 troops to the Confederate States Army. Its chief importance was in food-supply to the south, and support for blockade-runners, with its long coastline full of inlets, hard to patrol.
Document 15: Veteran's Monument in Covington: The Veteran's Monument, also called the War Between the States Veteran's Memorial, in Linden Grove Cemetery of Covington, Kentucky was built in remembrance of both Union and Confederate veterans of the American Civil War. It is one of only two memorials in the Commonwealth of Kentucky that celebrate soldiers of both sides of the conflict. The American Legion dedicated the monument on May 30, 1933, which was that year's Memorial Day.
ground_truth: Abraham Lincoln