Even though Maryland did not secede from the Union, Steuart's loyalty lay with the South, as did that of his father.
He commanded one of the Baltimore city militias during the riot of April 1861, following which Federal troops occupied Baltimore, an incident which was arguably the first armed confrontation of the Civil War.

Steuart resigned his captain's commission on April 16, 1861 and soon entered the service of the Confederate army as a cavalry captain.
He and his father were determined to do their utmost to prevent Union soldiers from occupying Maryland.
On April 22 Steuart wrote to Charles Howard, President of the Board of Baltimore Police:
"If the Massachusetts troops are on the march [to Annapolis] I shall be in motion very early tomorrow morning to pay my respects to them".

However, events did not move in their favor and, in a letter to his father, Steuart wrote:
"I found nothing but disgust in my observations along the route and in the place I came to – a large majority of the population are insane on the one idea of loyalty to the Union and the legislature is so diminished and unreliable that I rejoiced to hear that they intended to adjourn...it seems that we are doomed to be trodden on by these troops who have taken military possession of our State, and seem determined to commit all the outrages of an invading army."

Steuart's efforts to persuade Maryland to secede from the Union were in vain.
On April 29, the Maryland Legislature voted 53–13 against secession.
and the state was swiftly occupied by Union soldiers to prevent any reconsideration.
Steuart's decision to resign his commission and join the rebels would soon cost his family dear.
The Steuart mansion at Maryland Square was confiscated by the Union Army and Jarvis Hospital was erected on the estate, to care for Federal wounded.
However, Steuart was welcomed by the Confederacy as "one of Maryland's most gifted sons", and it was hoped by Southerners that other Marylanders would follow his example.
Even though Maryland did not secede from the Union, Steuart's loyalty lay with the South, as did that of his father. He commanded one of the Baltimore city militias during the riot of April 1861, following which Federal troops occupied Baltimore, an incident which was arguably the first armed confrontation of the Civil War.
Steuart resigned his captain's commission on April 16, 1861 and soon entered the service of the Confederate army as a cavalry captain. He and his father were determined to do their utmost to prevent Union soldiers from occupying Maryland. On April 22 Steuart wrote to Charles Howard, President of the Board of Baltimore Police:
"If the Massachusetts troops are on the march [to Annapolis] I shall be in motion very early tomorrow morning to pay my respects to them".
However, events did not move in their favor and, in a letter to his father, Steuart wrote:
"I found nothing but disgust in my observations along the route and in the place I came to – a large majority of the population are insane on the one idea of loyalty to the Union and the legislature is so diminished and unreliable that I rejoiced to hear that they intended to adjourn...it seems that we are doomed to be trodden on by these troops who have taken military possession of our State, and seem determined to commit all the outrages of an invading army." 
Steuart's efforts to persuade Maryland to secede from the Union were in vain. On April 29, the Maryland Legislature voted 53–13 against secession. and the state was swiftly occupied by Union soldiers to prevent any reconsideration. Steuart's decision to resign his commission and join the rebels would soon cost his family dear. The Steuart mansion at Maryland Square was confiscated by the Union Army and Jarvis Hospital was erected on the estate, to care for Federal wounded. However, Steuart was welcomed by the Confederacy as "one of Maryland's most gifted sons", and it was hoped by Southerners that other Marylanders would follow his example.
George H. Steuart (brigadier general)