The Battle of Westport was the largest engagement west of the Mississippi River in the Civil War, sometimes referred to as the “Gettysburg of the West”. In September, Sterling Price had launched an invasion of Missouri. All his units were mounted, as the infantry units intended to support him had been sent elsewhere, turning the invasion into more of a grand cavalry raid. Price called his force the Army of Missouri. On September 27th, Price suffered horrific casualties for no gain trying to capture Fort Davidson. The Union forces gathered to oppose Price well outnumbered him, but they had problems of their own. Price’s old adversary Maj. Gen. Samuel R. Curtis commanded the Department of Kansas; most of his men were Kansas militia who were extremely reluctant to cross the border into Missouri. Maj. Gen. William S. Rosecrans commanded the Department of Missouri; but he had to use most of his forces to block Price from his main targets, which he did successfully. Fighting several more largely pointless battles along the way, costing him precious time, he discovered that both St. Louis and Jefferson City were too heavily fortified for him to capture. Price decided to set out for Fort Leavenworth in Kansas, setting the stage for the showdown between Price and Curtis.
As Price’s men advanced west, Curtis sent a small detachment of his Army of the Border under Maj. Gen. James Blunt to slow him down. Without Curtis’ full force behind him, Blunt couldn’t stop Price, but he did slow him down and gain valuable information about his strength. A formidable detachment from Rosecrans’ forces closed on Price from the northeast, 10,000 Union cavalry under Alfred Pleasonton. They roughly handled part of Price’s army in the Second Battle of Independence, but John S. Marmaduke’s division managed to stalemate them, and Price’s army continued towards Westport, where Price had learned that Curtis had assembled his men.
Price was severely outnumbered by the total forces of his adversaries; Curtis had 12,000 men, Pleasonton around 10,000, and Price around 8,500, after the grievous casualties he had already suffered. Price accordingly decided to deal with his adversaries one-by-one. Pleasonton was hot on Price’s heels, so he decided to leave one division to hold off Pleasonton, and concentrate the rest of his forces on Curtis, whose forces had a very significant percentage of state militia to oppose Price’s veterans. Blunt, acting as the field commander for Curtis at the time, assembled the three brigades of his provisional division on good ground near Brush Creek, perpendicular to the state line, while a fourth marched to join him from Kansas City. He decided to open the engagement by sending skirmishers forward.
This provoked a full-scale rebel counterattack that sent one of his brigades reeling all the way over the state line, and another back into Westport itself. Disaster appeared imminent, but Shelby’s division was low on ammunition and stopped, and Blair’s brigade arrived from Kansas City. Meanwhile, Curtis could hear Pleasonton’s guns at Byram’s Ford nearby, and rode forward to personally direct Blair’s troops into battle. The Union forces charged across the creek again and up the ridge towards the rebels, but were repulsed. Curtis searched for a weak point so he could flank the enemy, and his scouts located a farmer who showed them a gulch that cut right past the rebel flank. Curtis led his headquarters escort and the 9th Wisconsin Artillery Battery through the gulch. Blunt pushed forward, slowly shoving back the Confederates until Curtis’ battery opened fire from the flank, enabling Blunt’s men to pour over the ridge they were attempting to ascend, and engage the Confederate at close range. A see-saw struggle ensued on the open prairie at the top of the ridge, with the Union forces finally managing to drive the Confederates back to the Wornall House.
Meanwhile, Pleasonton’s cavalry had caught up with Price’s rearguard under Marmaduke, and a cavalry battle ensued at Byram’s Ford along the Little Blue River, in Price’s rear. Pleasonton attacked Marmaduke with three of his four brigades, starting at 8:00 a.m. Pleasonton, not known for being an aggressive front-line leader back in the east, was driving his men hard this day, and even relieved one of his commanders, Egbert Brown, for stalling his attack against Marmaduke. He was replaced by Lt. Col. Frederick Benteen. Marmaduke initially held his own, but Pleasonton managed to seize the west bank of the Little Blue River at 11:00 a.m, and Marmaduke fell back to join Shelby and Fagan’s divisions. Blunt and Pleasonton began hammering the now-consolidated Confederates. At this point, Pleasonton’s fourth brigade crossed a ford at Hickman Mills, driving off a rebel brigade in the process, and attacked Price as well, meaning that the now-outnumbered old Missouri rebel was under attack from three sides.
The rebels pulled back to one final line of defense along the road south of Forrest Hill. Price only had one of his fourteen cannon remaining; the Union now mustered thirty guns, and Price no longer had the high ground. Pleasonton’s cavalry were located within easy range of the Confederate flank and rear, and seeing this, Curtis ordered an immediate general advance. After a brief attempt to capture a Union battery with a cavalry regiment, the Confederates were quickly broken, with the valiant Confederate Iron Brigade of Shelby’s division covering the retreat until it too was broken. Price’s men set fire to the prairie grass in an attempt to cover their withdrawal. Both sides suffered in the area of 1,500 casualties, reportedly; however, in the case of Price, he had been routed from the field, his artillery was gone, and he lost a much greater percentage of his troops. Curtis accurately reported that the victory had been most decisive. While most of the state militia would soon return home, Blunt and Pleasonton’s cavalry would chase Price all the back into Arkansas, ending the Army of Missouri as a significant threat for good. The campaign as a whole had been a Confederate bloodbath; Price entered Missouri with 12,000 men, and picked a few thousand more recruits from irregular forces in the state. When he departed Missouri for the last time with his army, he had maybe 6,000 left.