In European courts, pleadings emphasize factual allegations, issue formulation and proof at trial. US courts, even in antitrust cases, will permit cases to go forward on the basis of bare-bones pleadings. European courts require much more detail. It was first adopted in the US as part of the 1912 Equity Rules. When the Federal Rules of Civil Procedure were adopted in 1938, discovery was a key ingredient.
Discovery is intimately related to the concept of notice pleading.
The drafters of the Federal Rules believed that historically pleadings had played too large a role in federal litigation. In their view, the essential function of pleadings was simply to put the adversary on notice of the claims and defenses at issue. They saw no need for a detailed rehearsal of factual allegations at the outset of the case. The specifics of a claim could be fleshed out prior to trial through interrogatories, exchange of documents and depositions. The drafters also recognized that it would be difficult, if not impossible, for a plaintiff to prepackage its case prior to filing the complaint, especially where the facts were in the exclusive possession of the adversary.