As a general proposition it may be said that the states are independent of each other, and so far as they can have any relations to each other or to the citizens of another state those relations are determined by the provisions of the federal constitution. The laws of each state have force only within its limits. The extent to which rights and obligations arising within one state are to be recognized in another is determined in general by the same rules of comity which apply between foreign governments; that is, the states are said to be foreign to each other in deciding the effect to be given in one state to the laws of another.

Nevertheless, just as between governments entirely foreign to each other, so as between states, some principles obtain to which the term "private international law " or " conflict of laws " is usually applied. Thus contracts made in one state and valid where made are usually recognized as valid when it is sought to enforce or call them in question in another state. But the general subject of conflict of laws as affecting the validity of contracts, the liability for injury done to persons or property, the recognition of marriages and divorces in another state and like matters, are beyond the scope of this treatise.

The fact that the laws of one state cannot be enforced in another and that the authority of one state cannot be in any way exercised within the limits of another is to be especially borne in mind with reference to crimes against its laws. A crime is to be punished if committed against the laws of a state only within the limits of that state, and the courts of another state cannot take cognizance of such a crime for purposes of punishment; nor has any state the authority to send its officers into another state for the purpose of arresting and bringing back a fugitive from justice, save as provided by the federal constitution.