a separate sovereign within the U.S. federal system, and each therefore has its own laws on questions of marriage, inheritance, and liability for tort and contract actions. Persons who reside in the U.S. must have a state domicile for various purposes. For example, a person can always be sued in their state of domicile. Furthermore, in order for individual parties (that is, natural persons) to invoke the diversity jurisdiction of a United States district court (a federal trial court), all the plaintiffs must have a different state of domicile from all the defendants (so-called "complete diversity"). In 2010, the United States Supreme Court case of Hertz Corp. v. Friend concluded that the "principal place of business refers to the place where corporations' high level officers direct, control and coordinate the corporations' activities." A corporation's state of incorporation and principal place of business each count for (or against) diversity jurisdiction. Political office It is important in terms of politics, as in many jurisdictions candidates must maintain residency within the district in which they intend to run. Requirements vary by jurisdiction, and sometimes by the political office for which a person runs. The cutoff may be as little as a month or as much as several years. Once elected, the office-holder must remain resident in the appropriate district, or may usually be forced to resign. Canada To run as a candidate for election to the House of Commons of Canada, a candidate must have established residency in Canada — however, a person does not need to have established residency in the specific district where they are running. In most elections, in fact, virtually all of the major political parties run at least a few paper candidates in districts where they do not have a strong organization or a viable local candidate; a paper candidate may be from almost anywhere in the country. As well, when a political party with representation in the House of Commons selects a new leader who is not a sitting Member of Parliament, it is common for a member of that party's caucus to resign his or her seat so that the leader can run in the resulting by-election. The leader may, at their own discretion, continue to represent that district for the duration of their career in politics, or may run in a district closer to their home in the next election. As of 2012, for instance,