Ramadan --> Isn't being a "Sunni Muslim" imply that Islam is divided? Why don't we just be called Muslims...?

Sunni means follower of the Sunnah. ALL Muslims are to follow the Sunnah rendering ALL Muslims Sunni by definition. Its does not mean you are in a sect by follow the Sunnah. Are Shia not followers of the Sunnah also? Ergo what are they then? Sunni Shia's? I dont think so. I am a Muslim its not proceded with any word.