Davis's distinguished service in Mexico earned him high prestige at the outbreak of the Civil War, when he led Union troops through Southern Missouri to Pea Ridge, Arkansas, being promoted to Brigadier General after that significant victory.

Following the Siege of Corinth, he was granted home leave on account of exhaustion, but returned to duty on hearing of Union defeats in Kentucky, where he reported to General William "Bull" Nelson at Louisville in September 1862.

[1][2][page needed] Davis avoided conviction due to the shortage of experienced commanders in the Union Army, but the incident hampered his chances for promotion.

[8] When the war began in April 1861, Davis was an officer in the garrison at Fort Sumter when it was bombarded by Confederate forces.

After the death of Brigadier General Nathaniel Lyon and the loss at Wilson's Creek,[a] his request was gratefully accepted.

His experience as a regular in the federal army made him a rare commodity, and he was given command of the 22nd Indiana Infantry Regiment, receiving a promotion to colonel.

By the end of August, Davis received orders to succeed Brigadier General Ulysses S. Grant as commander of forces in northwestern Missouri.

Initially, Davis spent time building fortifications to fend off possible attack on the capital city.

[c] Davis's distinguished service at Pea Ridge was rewarded in May 1862 when he received a field promotion commensurate with his division command.

I find myself compelled by physical weakness and exhaustion to ask... for a few weeks' respite from duty...."[12] On August 12, 1862, the Army of Mississippi issued General Rosecrans' response in Special Order No.

The Army of the Ohio, commanded by Brigadier General Don Carlos Buell, was taking aim on Chattanooga, Tennessee.

Three hundred miles of railway lines lay between Louisville and Chattanooga, and Confederate forces were making constant work tearing up the tracks.

When Nelson arrived in Louisville, he found Major General Horatio G. Wright had been sent by the President to take control, putting Buell second in command.

[15] The two-day Battle of Richmond, ending on August 30, was an overwhelming Confederate victory in all aspects: Union casualties numbered over 5,000, compared to the 750 Confederate casualties, and considerable ground was lost, including Richmond; Lexington; and the state capital, Frankfort.

General James Barnet Fry, described as a close friend of Davis, was present and later wrote of the events surrounding the death of Nelson.

Nelson turned toward the Adjutant-General and said: "Captain, if General Davis does not leave the city by nine o'clock tonight, give instructions to the Provost-Marshal to see that he shall be put across the Ohio River.

[22] Davis arrived in Louisville in the afternoon on Sunday, September 28, and reported to the Galt House early the next morning, at breakfast time.

When Davis arrived and looked around the room, he saw many familiar faces and joined Oliver P. Morton, Indiana's governor.

The bullet hit Nelson in the chest and tore a small hole in the heart, mortally wounding the large man.

His trial by a court-martial or military commission should take place immediately, but I can't spare officers from the army now in motion to compose a court.

I was satisfied that Davis acted purely on the defensive in the unfortunate affair, and I presumed that Buell held very similar views, as he took no action in the matter after placing him in arrest.

[27] The charges never came possibly because larger events, such as the launching of Buell's campaign in Kentucky five days later, overshadowed the Davis-Nelson affair.

There was no trial or any significant confinement since it appears that Davis was staying at the Galt House without guard, as based partly on Wright's statement.

[26] Davis was a capable commander, but because of the murder of Nelson, he never received a full promotion higher than brigadier general of volunteers.

He, however, received a brevet promotion to major general of volunteers on August 8, 1864, for his service at the Battle of Kennesaw Mountain, and he was appointed commanding officer of the XIV Corps during the Atlanta Campaign, which he retained until the end of the war.

During Sherman's March to the Sea, Davis's actions during the Ebenezer Creek passing and ruthlessness toward former slaves have caused his legacy to be clouded in continued controversy.

As Sherman's army proceeded toward Savannah, Georgia, on December 9, 1864, Davis ordered a pontoon bridge removed before the African-American refugees, who were following his corps, could cross the creek.

[28] After the Civil War, Davis continued service with the army, becoming colonel of the 23rd Infantry Regiment in July 1866.

Davis gained fame when he assumed command of the US forces in California and Oregon during the Modoc War of 1872–1873, after General Edward Canby and Reverend Eleazer Thomas had been assassinated during peace talks.

[30] Davis's campaign resulted in the Battle of Dry Lake (May 10, 1873) and the eventual surrender of notable leaders, such as Hooker Jim and Captain Jack.