Statistics for occurrence #1 of “Pennsylvania” in chapter 1 of William Swinton, Campaigns of the Army of the Potomac:
...north and south, and its peculiar topographical relations, is an eminently aggressive line for a hostile force moving northward to cross the Potomac into Maryland, either with the view of penetrating Pennsylvania or of manoeuvring towards Washington.
It was by this line that Lee issued upon the soil of the loyal States on the occasion of both the Confederate invasions—to wit, the Maryland invasion of...
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