Plea bargaining in the United States
The constitutionality of plea bargaining was established by "Brady v. United States" in 1970, although the Supreme Court warned that plea incentives which were sufficiently large or coercive as to over-rule defendants' abilities to act freely, or used in a manner giving rise to a significant number of innocent people pleading guilty, might be prohibited or lead to concerns over constitutionality. "Santobello v. New York" added that when plea bargains are broken, legal remedies exist.
Pleading
In its final form in the 19th century, common law pleading was terribly complex and slow by modern standards. The parties would normally go through several rounds of pleadings before the parties were deemed to have clearly stated their controversy, so that the case was "at issue" and could proceed to trial. A case would begin with a complaint in which the plaintiff alleged the facts entitling him to relief, then the defendant would file any one of a variety of pleas as an answer, followed by a replication from the plaintiff, a rejoinder from the defendant, a surrejoinder from the plaintiff, a rebutter from the defendant, and a surrebutter from the plaintiff. At each stage, a party could file a demurrer to the other's pleading (essentially a request that the court immediately rule on whether the pleading was legally adequate before they had to file a pleading in response) or simply file another pleading in response.