Why arent shias muslim?

actually, Shias are muslims. but the problem is that nowadays people are trying to divide the Islamic nation and make it weak by creating differences between their mathaheb. the difference between Shias, Sunnis, Wahabis... is a minor difference that really doesn't matter. We all believe in Allah as God and we all believe in Muhammed as his messenger. So, people shouldn't go around saying this because it only causes hatred amongst all muslims which is the main goal for some people. But Islam will stay strong and muslims will still be united In Shaa Allah...