Deleting hundreds of Groups in Contacts???

I wanted to completely delete the contents of my Contacts which has ~4000 cards. I was able to Edit>Select All then delete all contacts. I then wanted to delete all the Groups in Contacts, of which I have hundreds.

Is there some way to select all of those and delete hundreds of those? I know I can delete them one at a time but that will take me a few days!!! It baffles me why Apple chose not to make deleting multiple Groups as easy as Select All>Delete like most other functions.

Is there a database in the Contacts Package or some other way to start a clean slate with Contacts without having to set up a new user account? Scratching my head about this one...