In Guns, Germs, And Steel chapter twelve Jared Diamond explains his theory of how the spread of writing was very influenced by geography (215). Geography is what kept certain places from being barbaric and it also determined when the shift from barbarianism to civilization occurred. First the writing spread by trade to the nearby areas then it spread to other places that those civilizations traded with. This is how writing spread, the reason it was not all adopted at once was because of distance and geographical barriers.
The fact of geography playing such a major role can be explained when you look at the civilizations that had a form of writing and also when the civilizations conceived this form of writing. The first civilizations to have a language was Sumer, the origin and then soon after it moved to Egypt a civilization that is fairly close and that does not have any geographical barriers to keep out influences from other civilizations. China is believed to have made their own original writing because of the large time difference and there are no other civilizations that used writing in-between Sumer and China (231).
It only appears that way though the reason for the time difference between the start of languages can be explained by the long and very tough journey between Sumer and China. The fact that there were no other civilizations that used writing is easily explained, it just comes down to that those civilizations did not want or need writing an example of this would be the Huns (215). Geography was what allowed writing to spread without barriers and easy routes writing would have spread very differently, these factors influenced the great civilizations and also kept other civilizations from becoming prominent.