Originally there wasn't even Buddhism, there was just the truth - the teachings of the Buddha. Since then, Buddhism has divided into a number of different systems.
The different systems accept many of the same fundamental teachings as correct and there is little friction between any of these groups - much less than is found among different groups of many other religions.
The best way to regard the different types of Buddhism is as alternative paths to enlightenment. Another way is to realise that while each type is found in many countries, each is strongest in particular parts of the world.