Price – Harney Truce The Price – Harney Truce was a document signed on May 21 , 1861 between United States Army General William S . Harney ( Commander of the U . S . Army ' s Western Department ) and Missouri State Guard commander Sterling Price at the beginning of the American Civil War . The truce sought to forestall the outbreak of violence in the state of Missouri following the Camp Jackson Affair , in which Union army troops under the command of Captain Nathaniel Lyon had captured Missouri State Militia mustered on the outskirts of St . Louis . While Lyon marched the captured militia to the St . Louis Arsenal through a crowd , a civilian riot ensued . The soldiers fired into the crowd and killed several people . In the aftermath of the riot , the Missouri State Legislature enacted the governor ' s " Military Bill " replacing the Missouri State Militia with a new Missouri State Guard . The governor appointed Sterling Price Major General and Commander of the State Guard . General Harney had been away from St . Louis during the Camp Jackson affair . Upon his return , he met with Price to sign a joint statement " for the purpose of removing misapprehensions and allaying public excitement , " its object being " that of restoring peace and good order to the people of the State in subordination to the laws of the General and State Governments . " The Price – Harney Truce made Federal forces responsible for order in the St . Louis area , and state forces responsible for order in the rest of the state . Under the terms of the truce , as understood by Harney , the agreement obligated the Missouri State Guard to protect Unionist Missourians from harassment and to hold the state for the Union . Harney also informed Price that several clauses in Missouri ' s recently enacted " Military Bill " would have to be modified to remove potential conflicts with the Federal Government ' s legal authority . The truce drew the immediate ire of a wide variety of Missouri Unionists ( including the politically powerful Congressman Frank Blair ) who lobbied President Lincoln and the War Department to have Harney relieved of command . In the face of reports of abuses against Missouri Unionists , and continued negotiations between Governor Jackson and the Confederate Government , Lincoln approved Harney ' s replacement as Commander of the Western District by newly promoted Brigadier General Nathaniel Lyon . The change of command took place on May 30 . Whereas Harney was recognized as a legalistic and cautious Unionist , Lyon was an outspoken Abolitionist , with a long - standing relationship with several militant Missouri Unionist organizations . Lyon ' s elevation effectively ended the truce with Price . On June 11 Missouri Governor Claiborne Fox Jackson held a last - ditch meeting at the Planter ' s House Hotel in St . Louis to delay open conflict in the State . Jackson was an open Confederate sympathizer and Price had been a conditional Unionist until the Camp Jackson Affair . During the meeting , Lyon angrily refused Price ' s requests to limit Federal forces to the metropolitan St . Louis area , and to disband " Home Guard " companies established by Missouri Unionists . Lyon refused to accept any limitations on his military actions in the state , and eventually halted the meeting , informing Governor Jackson and MG Price that such limitations on Federal authority " means war " . Price and Jackson returned to the State Capitol at Jefferson City , and worked to concentrate State Guard forces in anticipation of open warfare with Unionist forces . Three days later Lyon landed troops at the state capitol from steamboats and occupied the city without a shot fired . Lyon ' s mixed force of volunteers and Regulars subsequently routed the State Guard at the June 17 , 1861 Battle of Boonville which gave Unionist forces control of Jefferson City , the Missouri River line and the strategic North Missouri Railroad . In the absence of Governor Jackson , who had fled to the southern part of the state with the Guardsmen , the State Constitutional Convention called itself into session , declared the office of Governor vacant , and appointed Hamilton Gamble , former state Chief Justice , as Governor of the Provisional Government of Missouri . Gamble served from 1861 to 1864 , when he died in office . See also . Missouri Secession