three great nobles of the Meiji Restoration
Refers specifically to the three statesmen Okubo Toshimichi, Saigo Takamori, and Kido Takayoshi, who were instrumental in the Meiji Restoration. A historical term used in discussions of modern Japanese history.
The three great nobles of the Restoration are known as central figures of the Meiji Restoration.
The Meiji Restoration itself, the historical event; 維新の三傑 refers to the three key individuals within that event.
From 維新 (ishin, 'restoration', referring to the Meiji Restoration) + の (no, possessive particle) + 三傑 (sanketsu, 'three outstanding individuals'). The term is a historical designation for the three statesmen.