In Ponzi v. Fessenden (258 U.S. 254), the United States Supreme Court identified the issue as follows (at 259): "We live in the jurisdiction of two sovereignties, each having its own system of courts to declare and enforce its laws in common territory. It would be impossible for such courts to fulfill their respective functions without embarrassing conflict unless rules were adopted by them to avoid it. The people for whose benefit these two systems are maintained are deeply interested that each system shall be effective and unhindered in its vindication of its laws. The situation requires, therefore, not only definite rules fixing the powers of the courts in cases of jurisdiction over the same persons and things in actual litigation, but also a spirit of reciprocal comity and mutual assistance to promote due and orderly procedure." The United States Supreme Court then set forth the following rule (at 260): "The chief rule which preserves our two systems of courts from actual conflict of jurisdiction is that the court which first takes the subject-matter of the litigation into its control, whether this be person or property, must be permitted to exhaust its remedy, to attain which it assumed control, before the other court shall attempt to take it for its purpose."