The Constitution has proceeded upon a theory of its own, and given or withheld powers according to the judgment of the American people, by whom it was adopted. We (_i. e._ the Supreme Court) can only construe its powers, and cannot inquire into the policy or principles which induced the grant of them. The Constitution has presumed (whether rightly or wrongly we do not inquire) that State attachments, State prejudices, State jealousies, and State interests, might sometimes obstruct, or control, or be supposed to obstruct or control, the regular administration of justice. Hence, in controversies between States; between citizens of different States; between citizens claiming grants under different States; between a State and its citizens, or foreigners, and between citizens and foreigners, it enables the parties, under the authority of Congress, to have the controversies heard, tried, and determined before the national tribunals. No other reason than that which has been stated can be assigned, why some, at least, of these cases should not have been left to the cognizance of the State courts. In respect to the other enumerated cases—the cases arising under the Constitution, laws, and treaties of the United States, cases affecting ambassadors and other public ministers, and cases of admiralty and maritime jurisdiction—reasons of a higher and more extensive nature, touching the safety, peace, and sovereignty of the nation, might well justify a grant of exclusive legislation.[297] From the principle here given it may be deduced that cases or controversies in State courts are removable from them into federal courts if the case or controversy involves the Constitution, a treaty or an act of Congress.[298] But a prisoner in custody under the authority of a State should not, except in a case of peculiar urgency, be discharged by a court or judge of the United States upon a writ of _habeas corpus_, in advance of any proceedings in the courts of the State to test the validity of his arrest or detention.[299]