I have a very old and huge GIT repo. A long time ago a branch A was created that has been acting as a main development branch since its creation. Other branches were created to implement features - always taking branch A as a root and merged back into the branch A.
What I would like to do is to start a new GIT repository. The new repository would take the creation of the branch A as its beginning (the beginning of its history). Thus I would like to abandon the previous history.
I am not a GIT beginner but since this is something which is not a standard GIT operation I would like to ask you guys for any advice, ideas, useful links on how I can achieve what I have just described.
To keep my question short: How to start a new repo from a branch without losing a history of that branch and its child branches?