The splitting of the catholic and orthodox churches was called the

The Great Schism

A struggle over authority in the church led to mutual declarations of excommunication between the pope in Rome and the patriarch of Constantinople.  This break between Roman Catholicism and what became known as Eastern Orthodoxy is known as "The Great Schism.""Catholic" means universal -- the Roman pope was intent on asserting his leadership over all of Christendom.  "Orthodox" means "right teaching."  The Eastern patriarch and church were asserting their teachings to be right over against positions held in the West.  There were a number of doctrinal issues debated hotly between East and West over the centuries leading up to the schism.  But more than anything, the split came down to "church power" -- who held control over the church.