want to move to a single Active Directory

Currently we have a setup where there is one main doamain(mydomain.local) and 14 sub domains (domain1.mydomain.local, domain2.mydomain.local, etc…) Also there is a AD for each one… I want to be able to move to a scenario where I have 1 AD and can manage all users in the forest through one window instead of switching between the ADs and have one admin account instead of 15.
Please let me know if it is possible and if there is any good place to get some information on that. I looked around, but didn’t find anything 🙁