People from the outside has a tendency to over estimate the unity of other groups. For a long time, the first world nations thought all the Communist countries

People from the outside has a tendency to over estimate the unity of other groups. For a long time, the first world nations thought all the Communist countries were buddies but China had border wars with both the USSR and Vietnam. In the Islamic world, Muslim nations fought each other all the time as they still do today. In the Christian realms, the Crusades started with Western Christians sacking Constantinople and the wars of religion between the Catholics and Protestants were pretty brutal. France was at one point allied with the Turks during the period of the "Italian Wars". It tends to be that people think first of their own welfare and then maybe of their allegiance to the groups they belong to.