Matthew Page Andrews, M.A., Randall's literary executor offered these notes in his 1910 collection, The Poems of James Ryder Randall:

The despot's heel: — In order to appreciate this battle-hymn and its terms, we must understand the situation as seen by the poet from the Southern point of view. Beginning early in 1861, radical steps were taken by the Federal Government to suppress the pro-Southern sympathies shown by the people of Baltimore. These may briefly be summed up as follows: The suspension of the writ of habeas corpus; the proposed imprisonment of Chief Justice Taney; the midnight arrests and subsequent confinement, without charge or trial, of some thirty members of the State Legislature, besides a number of prominent citizens; the employment of spies and informers; the seizure and appropriation of private property; the arrests of clergymen; the suppression of newspapers; and the issuing of military orders, such as those directed against the Confederate colors, red and white, appearing in shop windows or the dress of children. All this and more seemed to Southern sentiment in Maryland as the “despot's heel,” indeed. Without the knowledge of these facts, from the Northern viewpoint it is natural that the terms of the poem should seem quite “overwrought and inaccurate.” Maryland found she could not serve two masters, however much her citizens might love the South while wishing to maintain the Union. (See Baltimore and the 19th of April, 1861, by Hon. George William Brown, Johns Hopkins University Studies in Historical and Political Science.)

Avenge the patriotic gore: — On the 19th of April a number of citizens were shot while obstructing the passage of the Sixth Massachusetts on the way south. Four of the soldiers and twelve citizens were killed, while scores were wounded. The bloodshed would have been much more serious, had not the Mayor of Baltimore arrived and placed himself at the head of the troops. (See Francis Folsom's Our Police, and the bibliography of Baltimore and the Nineteenth of April, 1861, prepared by Richard D. Fisher, who viewed the march as a “Union” sympathizer.)

Carroll, Howard: — These ready and apt references, from memory, to the gallant sons of his State show that the youthful poet was well versed in and deeply inspired by the story of their lives. Carroll's sacred trust was as a delegate to the Continental Congress that drew up the Declaration of Independence. John Eager Howard, lieutenant-colonel at the Cowpens, achieved national fame. Major Samuel Ringgold commanded the American artillery and was mortally wounded at Palo Alto. His gallant services very largely contributed to the winning of that brilliant victory. Colonel William H. Watson was killed while leading his regiment at Monterey. The fearless Lowe was Governor Lowe, who took a strong stand for the prerogatives of the State against the war measures of the Federal Government; as did Henry May.

And chaunt thy dauntless slogan song: — This verse was originally written “And add a new Key to thy song” but in later years, Randall, at the suggestion of several critics, notably O. W. Holmes, changed it to the present form. Dr. Holmes very properly observed that the pun, while a timely local hit, was “violative of true art.”

Sic semper: — Part of the motto of the “Old Dominion.” The close comradeship of the States of Maryland and Virginia was early illustrated in John Hammond's Two Sisters, Leah and Rachel, which appeared in 1656.

I hear the distant thunder-hum:— What a surpassing climax does this most spirited war-song attain in this last stanza! Here is summarized in a few lines the passionate appealing of the whole poem. The Old Line's bugle, fife, and drum epitomizes the chivalrous patriotism of the past in song and history. She is not dead, nor deaf, nor dumb — Huzza! She spurns the Northern scum. This is the poet's cry of greatest intensity, the impassioned call to arms reaching the topmost heights of triumphant anticipation. By some mistaken idea of false regard for sectional feeling, the Maryland societies have, in their publications, omitted this closing stanza of their State song.

We must concede the picture in the mind of the poet, formed but a single lifetime from the framing of the Constitution and its early interpretations, that Maryland could and would rise up in her might to throw off what was then regarded as an invasion on behalf of a newly arisen political party. The words themselves must be read in the spirit in which they were written, that of poetic imagery, and not interpreted in logical terms or narrow literalness. To the poet, Maryland was “a rock able to withstand a mighty sea of invasion and repel it in foam or scum at its base.” As for the invaders, the Massachusetts Sixth thought they were “enlisting for a picnic,” against opponents whom their poets described as the “soft-handed race who eat not their bread in the sweat of their face.” Who has yet suggested the omission of these and many other lines in the poems of Oliver Wendell Holmes (afterwards Randall's friend and admirer), because they might be sentimentally offensive to a section of the country? Or of Whittier's lines of intense appeal To Massachusetts, two stanzas of which are given here as containing some of Randall's terms:

It is safe to say that no brave member of the Massachusetts Sixth or of any Northern regiment would take offense at the expressions of a war-poem of opposite sympathies or expect it to be written in terms of perfect peace and amity. Publishers of the music of Maryland! My Maryland! have taken further liberties with the words, in which they cannot be justified. Randall's great war-poem should not be marred. What other has been so emasculated? In the oft-repeated call to “Maryland,” some have found with each repetition a varied appeal, more remarkable, because more frequent, than Poe's masterly use of “Nevermore.”

Maryland, My Maryland, Maryland, My Maryland and Other Poems, by James Ryder Randall, 1908, Page 17. (PDF)