It is true that small differences can mean large conflicts, but I think Catholicism and Eastern Orthodoxy is a better illustration of this. The only doctrine that the two denominations disagreed on was the exact way in which the Pope is higher-ranked than the other metropolitan bishops; this plus language barriers and differences in cultural atmosphere produced something like 1500 years of mutual hostility which were only ended by John Paul II.<p>However, we can sometimes mistake _subtle_ differences for _small_ ones; but just as there's a substantial difference between the Mac OS and Windows, there's a substantial difference between Catholicism and Calvinism (which was the most successful form of Protestantism) -- the difference between God seeing that you went to Hell, and God sending you there. I could go into much greater detail (I count nine paragraphs in how I'd previously structured this comment), but that's the nutshell of the nutshell.