Move folder to new repository and keeping history (inspired by https://gist.github.com/trongthanh/2779392)

gistfile1.txt

git clone <repourl>/repo-1.git 
cd repo-1
git remote rm origin # delete link to original repository to avoid any accidental remote changes
git filter-branch --subdirectory-filter dir-to-move -- --all # dir-to-move is being moved to another repo. This command goes through history and files, removing anything that is not in the folder.  The content of this folder will be moved to root of the repo as a result.
git tag -d $(git tag -l) # remove all tags from the old repository - history should now be clean
git remote add master ../new-repo/ # add the link to the new repo
git push # the new repo has just the moved folder including the history inside