American Security & Trust Co. v. District of Columbia Comm'rs
In American Security & Trust Co. v. District of Columbia Comm'rs, 224 U. S. 491 (1912), the Court concluded that a congressional Act applicable solely to the District of Columbia was not a "law of the United States" for purposes of paragraph six.
Mr. Justice Holmes' opinion for the Court reasoned that "all cases in the District arise under acts of Congress and probably it would require little ingenuity to raise a question of construction in almost any one of them." By restricting paragraph six to laws of national scope, the Court thought that its jurisdiction would be "confined to what naturally and properly belongs to it." Id., at 494-495.