So it has been held that a justice of the peace in the District of Columbia is an officer of the government of the United States, and is therefore exempt from militia duty. _Wise_ vs. _Withers_, 3 Cranch, 331; 1 Cond. Rep. 552. A citizen of the District of Columbia is not a citizen of any one of the United States. _Hepburn et al._ vs. _Ellery_, 2 Cranch, 445; _Westcott’s Lessee_ vs. _Inhabitants ----_, Peters, C. C. R. 45. Up to the time of the cession, the inhabitants of this District were under two jurisdictions--that of Maryland and that of Congress; but after the cession, under that of Congress alone. Now, when the inhabitants of this District passed out of the jurisdiction of Maryland, and came under the exclusive jurisdiction of Congress, let us see what was the effect of such change of jurisdiction upon them. In the act of Congress of 1790, c. 28, sect. 1, which was an act for establishing the seat of government of the United States, there is the following clause: “_Provided, nevertheless_, That the operation of the laws of the state [of Maryland] within such District shall not be affected by this acceptance, _until the time fixed for the removal of the government thereto, and until Congress shall otherwise by law provide_.” Here, then, Congress _expressly_ provided and contracted with the state of Maryland, that the laws of Maryland in this District should not be interfered with until the removal of the seat of government to this place; and Congress likewise _impliedly_ provided and contracted, that when the seat of government should be removed to this place, it would discharge the duty imposed upon it by the constitution of the United States, and would assume and exercise the “exclusive legislation” provided for in that instrument. This act of Congress was approved on the 16th of July, 1790. By the Maryland laws of 1791, c. 45, sect. 2, that state ceded to the United States the territory which now constitutes the District of Columbia, and the words of the cession are these: “In full and absolute right, as well of soil as of person, residing or to reside thereon,” &c. ... provided that the jurisdiction of the laws of Maryland “shall not cease or determine _until Congress shall by law provide for the government thereof_.” The state of the case, then, was simply this: 1. The constitution gave Congress power of “exclusive legislation” over such district as might be ceded for the seat of government. 2. Congress, by the act of 1790, above referred to, proposed to the state of Maryland to accept a portion of her territory for this purpose, but engaged not to interfere with her laws until after it had taken actual possession of the ceded territory. 3. Maryland accepted the proposition, rehearsing the condition in these words; namely, that “the laws of Maryland shall not cease or determine until Congress shall by law provide for the government thereof.”