I think that actions are motivated by emotions, when not motivated directly by instinct without thought. Some emotions thus produce an instinctive reaction, such as fear producing the action resultant of fight or flight. Unity is an action and hence requires a prerequisite emotion to motivate towards the instinctive reaction to the emotion.
There is nothing that creates unity more than a shared enemy. This is why this nation always embarks upon a campaign of demonizing an entity in order to first make it out as a threat/enemy and hence use the fear generated by the campaign to promote unity for an attack. Unlike the government, black folks really do not have to INVENT or embellish an enemy, we have 300 plus years of empirical evidence that should make us damn scared.
What keeps black folks from unifying is that we cannot see the forest due to the trees. In other words, we are not seeing the big picture of what is and has and is happening to black people the world over to put two and two together. Moreover, we see other black folks as being different and hence we do not link their suffering as part of the global black plight that is the consequence of white supremacy. Therefore, the problems of Africa or Haiti are not black problems resulting from the legacy or contemporary white manipulation or reaction; rather, they are seen as African and Haitian issues....and many of us look down upon them as inferior and not victims of the same external forces that we are in America.
Black unity will require not following the trend of America to be ahistorical, which removes the evidence that reveals an enemy. We also must start seeing other black folks around the world as "black like us" and hence see their suffering as our suffering....which will add urgency to the need for black unity to rise from under the foot of white supremacy.