If you are interested in researching the history of U.S. practice in international law, or the history of U.S. diplomacy more generally, there are several resources in HeinOnline and in ProQuest Congressional that can help you.
U.S. practice in international law is summarized in three editions of the Digest of International Law of the United States, each known more familiarly by the name of its editor. The first edition, edited by Moore, covers the years 1776-1904. The second edition, edited by Hackworth, covers the years 1905-1940. The third edition, edited by Whiteman, covers the years 1941-1972. These three editions have been updated by Digest of United States Practice in International Law, 1973-1981, and 1989 to present, and by the Cumulative Digest of United States Practice in International Law, which covers the years 1981-1988.
All of these digests are available in HeinOnline’s Foreign & International Law Resources Library, and easy to search. Suppose you wanted to find a discussion of the Halibut Fisheries treaty of 1930. Using the Advanced Search interface, you would simply search for the phrase “halibut fishery” in Hackworth. This search would retrieve a discussion of the treaty, its predecessor and successor treaties, with links to the texts of the treaties themselves.
You can also search for diplomatic correspondence and other documents relating to U.S. international affairs in Foreign Relations of the United States (FRUS), which is also available in its own library in HeinOnline. Here you could find all diplomatic correspondence related to the 1930 treaty on the “preservation of the halibut fishery of the northern Pacific and Bering Sea.” The trick to using the FRUS database is to realize that dates of coverage are not the same as dates of publication. Thus, to search for documentation from 1930 you would actually date-restrict your search to 1945, the year in which volumes for the year 1930 were published.
FRUS covers the history of U.S. foreign policy from 1861 onward. From 1817-1861, diplomatic correspondence and other documents relating to foreign relations were published in the Serial Set, a massive series best known as the source of Senate and House reports. The Serial Set is fully digitized and readily available electronically through ProQuest Congressional. The Serial Set is not difficult to search in ProQuest Congressional, but there is also a three-volume Index to United States Documents Relating to Foreign Affairs, 1828-1861, which is available in HeinOnline, in Spinelli’s Law Library Reference Shelf. If you were interested in the history of U.S/French trade relations in the nineteenth century, you could search this source for “France trade”~25 (the term ‘France’ within 25 words of the term ‘trade’), which would retrieve 14 items, among them an 1860 message from the president transmitting to Congress a letter from the emperor of France on commerce and free trade. This entry is accompanied by a citation to the Serial Set, 36. 1. H. ex. doc. 30, which you could use to retrieve the full text of the document in ProQuest Congressional.
The digests of U.S. practice of International law, Foreign Relations of the United States, and the Serial Set are the most important sources of information relating to the historic practice of the United States in international law and foreign affairs generally. All three readily available to researchers in HeinOnline and ProQuest Congressional.