History

git cloned a remote repository and made many changes pushing them all to
said repository over many months.

The powers that be then required me to move project to new repository
server did so by pushing local version to new remote saving all history!

Now have to merge back to original repository(which has undergone many
changes since I split off) but how do I do that without loosing the
history of all the commits since the original move?  Note I need to push
changes to files that are already in existence.  I found on the web a
bunch of ways to insert a whole new directory structure into an existing
repository but as I said I need to do it on top of existing files.  Of
course I can copy all the files from my local working repository to the
cloned remote repository and commit any changes but I loose all the
history that way.

Thanks.