For the Orthodox, church history is important, since Orthodoxy claims to be in the apostolic succession, i.e., institutionally descended from the apostles of Christ. You can find some pages about the history of Orthodoxy subordinated under this page using the menu above.
The split within Orthodoxy in modern times between the modernist/ecumenist versus the traditionalist movements began with the institution of the “New Calendar” over against the original church calendar which used the Julian calendar. The new calendar re-aligned the Church feast days with the contemporary secular calendar, the Gregorian calendar. Traditionalists regarded the change as an innovation in support of the ecumenist movement. Ecumenism is the larger issue.
Click here for a history of the Old Calendar / New Calendar split.