Suggested starting point: Chapter 20 of Oxford Handbook of the History of International Law
In the 1850s, Japan reappeared on the international stage after two centuries of deliberate isolation (sakoku) as the result of US "gunboat diplomacy."
1854 Treaty of Kanagawa.(Japan & USA)
Treaties of Peace, Amity, and Commerce with USA, Britain, France, Holland, and Russia (collectively the Ansei treaties)