Can we debug this by doing it piecemeal?
First, get your leader to work with an existing civilization.
Second, make your units "default" units that anyone can build.
Third, make your units unique units for an existing civilization.
If you didn't find any bugs or issues in the above stage, then we start attacking the civilization itself. Create a "stub" civilization (with as few properties as possible), and see if you can get it to show up.