Why are there so many "variations" on the Christianity theme?

Christianity began with 12 Apostles, so you have 12 vines to begin with, then as the centuries went by and empires rose and fell, societies and communities were separated and rejoined. Man, 2000 years is a long long time. When the renaissance came and then the scientific revival and the separation of England from Catholic Rome was realized, many righteous people existed in those times when the suffering in people became most evident and clic. The monastic life in England took a beating and the peasantry became more like slaves than citizens. Then America was discovered and all hell broke loose.