The lyrics are from a poem by James Ryder Randall. The first stanza is :
The despot's heel is on thy shore,
His torch is at thy temple door,
Avenge the patriotic gore
That flecked the streets of Baltimore,
And be the battle queen of yore,
So who was the despot in the song?
Update: Answer: The Union! Maryland was a border state, with the northern boundary defined by the Mason-Dixon line. It is truly "American in Miniature" with beaches, rural farmland, big cities and suburbs, and mountains. In the Civil War, troops were sent to both sides. Today, Maryland is a blue state, but only Baltimore and 3 of the 23 counties consistently vote blue. The remainder vote red, but are far less populous.
Here's a quote from the Maryland Manual about the state song:
"Maryland, My Maryland" was adopted as the State song in 1939 (Chapter 451, Acts of 1939; Code State Government Article, sec. 13-307).
The nine-stanza poem, "Maryland, My Maryland," was written by James Ryder Randall in April 1861. A native of Maryland, Randall was teaching in Louisiana in the early days of the Civil War, and he was outraged at the news of Union troops being marched through Baltimore. The poem articulated Randall's Confederate sympathies. Set to the traditional tune of "Lauriger Horatius" ("O, Tannenbaum"), the song achieved wide popularity in Maryland and throughout the South.