You can use --allow-unrelated-histories to force the merge to happen.

The reason behind this is that default behavior has changed since Git 2.9:

"git merge" used to allow merging two branches that have no common base by default, which led to a brand new history of an existing project created and then get pulled by an unsuspecting maintainer, which allowed an unnecessary parallel history merged into the existing project. The command has been taught not to allow this by default, with an escape hatch --allow-unrelated-histories option to be used in a rare event that merges histories of two projects that started their lives independently.

See the Git release changelog for more information.

More information can be found in this answer.

I ended in the same situation after a series of mishapps. Have a look at this thread : I just did a 

git pull --allow-unrelated-histories

and it was fixed!

You can use --allow-unrelated-histories, as morty answered. But watch out: this may not do what you want. It depends on what you want, and what's in the two commits you'll choose this way.

git merge works by comparing the merge base commit with the two particular other commits that you select. You select one of the two commits you want to use by checking it out:

git checkout master

and the other with an argument to git merge:

git merge wip269

for instance.

The merge base, however, is determined by the history, and history, in Git, consists of the commits in the repository, as linked by those commits themselves. This is where the command is failing, because the histories are not related to each other: there is no merge base commit.

If the histories were related, this:

          A--B--...--H   <-- master
         /
...--o--*
         \
          P--Q--...--W   <-- wip269

might be a good way to draw the commit graph. From this drawing, you could see that the history in master starts (or ends) at commit H and works backwards to A, and then to commit * and further back; and history in wip269 starts (or end) at commit W, then works back to P and on to * and further back.

Commit * would then be the merge base. The merge base is defined as the best common commit. The best one is obviously *—commits that come before it would work too, but it seems better to stick with the one closest to the two branch-ends you started from. The way git merge works is to compare the files in the merge base to the files in your current commit—here H—to see what you changed, then compare those same files in the same merge base to the files in their commit (W) to see what they changed. Having found what you both changed, Git can combine the changes.

The problem here is that your history does not look anything like this. It probably looks something like this:

A--B--...--H   <-- master (HEAD)

P--Q--...--W   <-- wip269

That is, starting at H and working backwards, Git eventually arrives at commit A, which is a root commit: it has no previous history. Meanwhile, starting at W and working backwards, Git eventually arrives at commit P, which is also a root commit. There is no shared commit that is on both branches.

Using --allow-unrelated-histories tells git merge: OK, if there's no common commit, play a pretend game that there is: pretend that there is a common commit that contains no files at all, and use that as the merge base.

This means that what you changed is: you invented every file from scratch. Meanwhile, what they changed is that they, too, invented every file from scratch.

Where the invented files have different names, Git will take the new files. Where they have the same names, Git will declare an add/add conflict and leave you to figure out what should go in the file with that name.

If and when you resolve all such conflicts and commit—or if there are no conflicts—Git will make a new merge commit whose parents are both H and W:

A--B--...--H
            \
             X   <-- master (HEAD)
            /
P--Q--...--W   <-- wip269

and now commits P through W are on both branches. Commits A through H, plus X, are (only) on master. If you move the name wip269 so that it, too, points to new commit X, all 17 commits will be on both branches; or you can delete the name wip269 now, if you're done with it, after which all commits are only on master.

Side note on git pull

All git pull does is run git fetch, then immediately run a second Git command. The second command is usually—and is in your case—git pull. So you can do this with git pull (which can pass --allow-unrelated-histories to its git merge), but you might as well do it with git merge at this point—you've probably already done any necessary fetch.

• I have a local and a remote repository and the local repository points to the remote repository.

  More specifically, you have a local tracking branch:

Remote-tracking branch names take the form <remote>/<branch>. For instance, if you wanted to see what the master branch on your origin remote looked like as of the last time you communicated with it, you would check the origin/master branch.

• When I ran the above command, the file .gitignore was downloaded into my local repository, but what else the above command does?

git pull runs git fetch with the given parameters and then depending on configuration options or command line flags, will call either git rebase or git merge to reconcile diverging branches.

So apparently, ".gitignore" was the only (committed) change between your remote and your local repos at that time.

I suspect "--allow-unrelated-histories" was both unnecessary, and probably irrelevant to understanding what actually happened:

By default, git merge command refuses to merge histories that do not share a common ancestor. This option can be used to override this safety when merging histories of two projects that started their lives independently. As that is a very rare occasion, no configuration variable to enable this by default exists and will not be added.

Only useful when merging.

The "official" Git documentation is on-line: Git Reference

Here's book I always keep by my side: Git in Practice, Mike McQuaid.

this happens when your local repo and the remote repo have different root commits (separate histories). if you are sure you want to combine them, run:
git pull origin main --allow-unrelated-histories
Resolve any conflicts, commit the merge, then push:
git push origin main
if you intended your local repo to exactly match the remote (and you don’t need local commits), the safer approach is to discard the local history and re-clone the remote repository instead.