be checked via collateral attack: when a plaintiff sought recovery against a defendant's assets in another state, that state could refuse judgment on the grounds that the original judgment was invalid. Difficulties in applying Pennoyer territorial jurisdiction Following Pennoyer, extreme applications of territorial jurisdiction revealed imperfections in the doctrine, and societal changes began to present new problems as the United States' national economy became more integrated by increasingly efficient multi-state transportation technology and business practices. While determining the physical location of an individual for the purposes of in personam jurisdiction was easy enough, applying the same principle to non-physical entities became difficult. Courts were presented with the question of where a company was present and amenable to service for the purpose of in personam jurisdiction over the company. Extension of quasi in rem jurisdiction led to extreme results that threatened the justification for the jurisdiction. Bearing in mind that territorial jurisdiction existed in a pre-industrial society where transportation across the country was difficult, long, and potentially treacherous, and consider the hypothetical wherein Alice owes Bob money, and Bob owes Carmel, a resident of New York, money. Carmel seeks to recover on Bob's debt to Carmel, however cannot do so because Bob avoids Carmel by traveling to California. Alice, however, happens to travel through New York. Carmel serves notice upon Alice, and attaches Alice's debt to Bob (considered to be property within the state) to the proceeding. Alice can no more certainly provide notice to Bob in California than Carmel could provide, and the transient and involuntary exposure of Bob to being hauled into court in New York by this attachment seems to erode the original rationale of quasi in rem jurisdiction. The US Supreme Court largely abolished the exercise of jurisdiction on the basis of quasi in rem in Shaffer v. Heitner, except in exceptional circumstances, which sometimes would arise while dealing with real property such as land, and when the owner of the land cannot be found. Modern Constitutional doctrine: International Shoe doctrine In the modern era, the reach of personal jurisdiction has been expanded by judicial re-interpretation and legislative enactments. Under the new and current doctrine, a state court may only exert personal jurisdiction over an individual or entity with "sufficient minimal contacts" with the forum state such that the particular suit "does not offend 'traditional notions of fair play and justice.'" The "minimum contacts" must be purposefully