Why did the eastern and western churches differ (medieval ages)

Medieval Christendom was divided into two parts. The Christians of eastern Europe were under the leadership of the patriarch of Constantinople (modern day Istanbul, in Turkey). Those in western Europe (which this article mainly deals with) were under the leadership of the bishop of Rome, commonly called the pope (papa, or "father"). These two branches gradually adopted different practices - for example the Western church came to ban clerical marriage, while the Eastern church did not - and there was growing friction between the two. Eventually, with the pope claiming seniority over the patriarch, and vice versa, both sides excommunicated each other in 1054. This began a schism which would last throughout the Middle Ages and beyond.

The Catholic Church of western Europe

In western Christendom, the Catholic Church remained a central institution throughout the Middle Ages. It controlled vast amounts of wealth - it was the largest landowner in Europe, and the people paid a tenth of their income - the “tithe”  - to the Church each year. Churchmen virtually monopolised education and learning. Bishops and abbots acted as advisors to kings and emperors. The pope claimed (and used) the power to ex-communicate secular rulers, and free their subjects from their oaths of obedience to him - powerful weapons in a deeply religious age. Through its network of parishes reaching into every town and village in western Europe, the Church constituted an extraordinarily powerful propaganda machine. Medieval kings ignored the Church's agenda at their peril.

Furthermore, the Church exercised exclusive jurisdiction over a wide range of matters: incest, adultery, bigamy, usury and failure to perform oaths and vows, matrimonial cases, legitimacy of children. All these were dealt with in Church, not secular, courts. 

As an all embracing multinational institution, the Church in fact formed an alternative focus of loyalty within western Christendom. All churchmen, however humble, enjoyed immunity from secular courts. Members of the clergy, who formed a small but significant minority within the population (between 1 and 2 per cent), looked to their bishops and archbishops, and above them to the pope, for leadership as much as to their kings.

after the french-indian war.