However, the bushwhackers held a special hatred for the "red leg" Union troops from Kansas who frequently entered Missouri and earned a reputation for ruthlessness.

Younger rode with Quantrill in a retaliatory raid on Lawrence, Kansas on August 21, 1863, during which about 200 citizens were killed and the town looted and burned.

He claimed he was sent to California on a recruiting mission, and returned after the war's end to find Missouri ruled by a militant faction of Unionist Radicals.

State authorities believed that Clement planned and led the first daylight peacetime armed bank robbery in U.S. history when he held up the Clay County Savings Association on February 13, 1866.

The first mention of their involvement came in 1868, when authorities identified Cole as a member of a gang that robbed Nimrod Long & Co., a bank in Russellville, Kentucky.

Former guerrillas John Jarrett (Younger's brother-in-law), Arthur McCoy, and George and Oliver Shepard were also implicated.

[2] Witnesses repeatedly gave identifications that matched Cole Younger in robberies carried out over the next few years, as the outlaws robbed banks and stagecoaches in Missouri and Kentucky.

On July 21, 1873, they turned to train robbery, derailing a locomotive and looting the express car on the Rock Island Railroad in Adair, Iowa.

[citation needed] Following the robbery of the Iron Mountain Railroad at Gad's Hill, Missouri in 1874, the Pinkerton National Detective Agency began to pursue the so-called James–Younger Gang.

Another Pinkerton agent who pursued the James brothers, W. J. Whicher, was abducted and later found dead alongside a rural road in Jackson County, Missouri.

[citation needed] The James and Younger brothers survived capture longer than most Western outlaws because of their strong support among former Confederates.

Cole Younger and his brother Bob both later said that they selected the bank because of its connection to two former Union generals and Radical politicians, Benjamin Butler, a Democrat, and Adelbert Ames, a Republican.

Younger and his brothers began to fire in the air to clear the streets, but the townspeople (shooting from behind cover, through windows and around the corners of buildings) opened a deadly fusillade, killing gang members Clell Miller and William Chadwell and badly wounding Bob Younger through the elbow.

They and another gang member, Charlie Pitts, waged a gun battle with a local posse in a wooded ravine along the Watonwan River west of Madelia, Minnesota.