

In the Middle Ages, efforts were made in order to establish a single Christian state of Pan-Christianity by uniting the countries within Christendom. Christian nationalism may have played a role in this era in which Christians felt the impulse to recover lands in which Christianity flourished. Muslims militarily invaded parts of North Africa, East Asia, Southern Europe, Central Asia, and the Middle East, as well as parts of Europe. In response, Christians across national borders mobilized militarily and a "wave of Christian reconquest achieved the recovery of Spain, Portugal, and southern Italy, but was unable to recover North Africa nor—from a Christian point of view, most painful of all—the Holy Land of Christendom."
Major religions in the past, especially Christianity, have attempted to include all their adherents in a large union, but they have not been successful. Throughout most of the Middle Ages in Western Europe, attempts were made again and again to unite all the Christian world into a kind of Pan-Christianity, which would combine all Christians in a secular-religious state as a successor to the Roman Empire.
Throughout the better part of the Middle Ages, elaborate attempts were made to create what was, in effect, a Pan-Christianity, an effort to unite "all" the Western Christian world into a successor state of the Roman Empire.