An Excerpt from "People & Events, The Civil War and emancipation, 1861 - 1865"
Black recruiters, many of them abolitionists such as Frederick Douglass, Henry Highland Garnet, and Mary Ann Shadd Cary, brought in troops from throughout the North. Douglass proclaimed, "I urge you to fly to arms and smite with death the power that would bury the government and your liberty in the same hopeless grave." Others, such as Harriet Tubman, recruited in the South. On March 6, 1863, the Secretary of War was informed that "seven hundred and fifty blacks who were waiting for an opportunity to join the Union Army had been rescued from slavery under the leadership of Harriet Ross Tubman...." By the end of the war more than 186,000 black soldiers had joined the Union army; 93,000 from the Confederate states, 40,000 from the border slave states, and 53,000 from the free states.
Source: "People & Events, The Civil War and emancipation, 1861 - 1865", PBS.org
Link to the full article: http://www.pbs.org/wgbh/aia/part4/4p2967.html
During the Civil War, President Abraham Lincoln's Emancipation Proclamation of 1863 freed slaves in Confederate states but not in the Union state of Maryland. Indeed, Maryland's Constitution of 1851 had forbidden passage of "any law abolishing the relation of master or slave, as it now exists in this State" (Art. 3, sec. 43). To end slavery, Maryland had to write a new constitution.
Governor Augustus W. Bradford, in his annual message of 1864 to the General Assembly, sought passage of a constitutional convention bill. The predominantly Unionist legislature promptly complied, and the electorate approved the call for a convention (Acts of 1864, ch. 5).
Delegates to the Constitutional Convention of 1864 were elected by the voters on April 6, 1864. The convention convened in Annapolis on April 27, 1864, and adjourned on September 6, 1864. The third state constitution, which abolished slavery in Maryland, received approval of the voters on September 18, 1864, and took effect November 1, 1864.
Source: Archives of Maryland Historical List Constitutional Convention, 1864
LInk to the source: http://www.msa.md.gov/msa/speccol/sc2600/sc2685/html/conv1864.html
This engraving features African Americans being guided onto a troop train headed for Murfreesboro where their wish to join the Federal Army will be granted. This illustration appeared in Frank Leslie's post-war volume "The Soldier in Our Civil War" (which has a number of editions), but it most probably premiered in "Frank Leslie's Illustrated Newspaper" during the actual conflict.