Slavery was under assault in the late spring and early summer 1861 from the acts of individual Union soldiers, the slaves themselves, and even members of Congress. Of the loyal slave states, none was more affected during this period than Maryland. As Union troops gathered in Northern Virginia to march on Richmond and prevent the rebel Congress from meeting, they often traveled through Maryland on their way south. Some slaves escaped into their camps, finding refuge and employment as personal servants or in other capacities.
Not surprisingly, Maryland slaveholders reacted with outrage, especially Unionists who had remained loyal and believed the Lincoln administration had a legal obligation under the Fugitive Slave Act to return their property. One of the most influential was Charles Benedict Calvert, U.S. Representative from Maryland’s Sixth District, a member of the state’s prominent Calvert family, and the founder of what became the University of Maryland (go Terrapins!). Having witnessed the U.S. House the day before vote that the army had no obligation to recapture fugitive slaves (and voted against the resolution), on July 10, 1861, George Calvert wrote President Lincoln with the complaints of Marylanders against federal troops.
While he also bemoaned the searches conducted by the Union army against citizens suspected of rebel sympathies, the bulk of Calvert’s letter addressed the army and escaped slaves. On this issue, he wrote:
To judge from the actions that began to emanate from the Lincoln administration, Congressman Calvert’s letter had an impact. Abraham Lincoln was well aware of the necessity of holding Maryland within the Union, as the state surrounded Washington, D.C. on three sides, the fourth side facing Confederate Virginia across the Potomac River. Lincoln had exerted much pressure on the state to forestall secession after the war started and on April 27, 1861, had taken the highly controversial step of suspending habeas corpus in Maryland. Having tightened the screws on Maryland, the President recognized the need to placate as well as coerce the state’s slaveholders, and did not support the House Resolution of July 9, 1861. These efforts will be dealt with soon in another edition of Civil War Emancipation.
Source: http://hd.housedivided.dickinson.edu/node/37349