One of the most common Git errors, "fatal: refusing to merge histories" occurs when there is an attempt to merge unrelated projects in one branch. This happens because the pull request or clone is not compatible with the commit histories and tags of a branch.
Resolving this error is not that difficult, though. The causes that lead to this problem and the solutions for it are presented below. The more intriguing question may be, would it be possible to stop this error from happening in the first place?