Unity is not about having no differences
but it is about tolerating them.
Think about it.
People are always calling for "the ummah" to "unite" and generally set out new places and positions to unite, telling them to leave the bickering of old.
But what these people don't understand is that there have been differing opinions and views from the start - going as far back as the first caliph and how to deal with the insurgent tribes in Arabia or even earlier to how to elect a new leader.
When Muslims have been united, it has not been because there have been no differences - rather because they weer tolerant of them, allowing others to have diferring views.