It might be an attempt at central rule but there would just be too many people... So you'd need regions with regional leaders underneath the control of the main authority (president? coalition government? huge bot?) anyway in order to attempt some semblance of control...
Guess what, the regions would start to form identities, people would move to the one that most pleases them, and will shun/ignore/pity the people from the most displeasing regions...
People also love finding groups of a nice manageable size in order to identify with.
I'm afraid even if we managed a "one world" that we'd just have countries anyway, under a different heading...