In order for a civil trial to take place, whether judged by a jury or solely by a judge, both parties must submit to the jurisdiction of the court, i.e. the government. (And a Judge is employed by, and is most certainly a part of, the government. Check out Article Three of the Constitution).
"Jurisdiction" in layman's terms mean submitting to the power of the government, with said power at its most basic level being regulated by the Constitution.
Hopefully this clears things up for you.
@Kara: unfortunately I only had the pleasure of living in London as a wee lad, so I can't answer that question from direct experience. But I'd be happy to take a stab at those questions in another thread, I think you started one a while back about this.