Whistleblowing website WikiLeaks has published more than 1.7 million US records covering diplomatic or intelligence reports on every country in the world.
Much of the work was carried out by WikiLeaks founder Julian Assange during his time in the Ecuadorian Embassy in London, where he has been staying since last summer.
He sought refuge at the embassy last June over fears that he would be sent to the United States if he was extradited to Sweden to face sexual offence claims by two women, charges that he denies.
The Ecuadorian Government has granted Mr Assange political asylum and has repeatedly offered Swedish prosecutors the chance to interview the Australian at the embassy, which is based in London's Knightsbridge area.
The data released today comprises more than 1.7 million US diplomatic records from the beginning of 1973 to the end of 1976, covering a variety of diplomatic traffic including cables, intelligence reports and congressional correspondence.
WikiLeaks has called the collection the Public Library of US Diplomacy (PlusD), describing it as the world's largest searchable collection of US confidential, or formerly confidential, diplomatic communications.
Mr Assange told the Press Association that the information showed the "vast range and scope" of US diplomatic and intelligence activity around the world.
Henry Kissinger was US Secretary of State and National Security Adviser during the period covered by the collection, and many of the reports were written by him, or were sent to him.
Thousands of the documents are marked NODIS (no distribution) or Eyes Only, as well as cables originally classed as secret or confidential.
Mr Assange said WikiLeaks had undertaken a detailed analysis of the communications, adding that the information eclipsed Cablegate, a set of more than 250,000 US diplomatic cables published by WikiLeaks from November 2010 and over the following year.
These documents were released after being anonymously leaked, detailing US foreign policy over the last decade.
The collection published today has not been leaked, but Mr Assange said WikiLeaks had been working for the past year to analyse and assess a vast amount of data held at the US national archives before releasing it in a searchable form.
Mr Assange said WikiLeaks had developed sophisticated technical systems to deal with "complex and voluminous" data.
Top secret documents were not available, while some others were lost or irreversibly corrupted for periods, including December 1975 and March and June 1976, said Mr Assange.
He added that his mother, who lives in Australia, had told him he was being kept at the embassy "with nothing to do but work on WikiLeaks material".