title: Merge between two git repositories?
body: <p>I have two repositories <strong>A.git</strong> and <strong>B.git</strong>. They are completely separate (do not share any common ancestor).</p>
  
  <p>Now I can merge changes from a branch in <strong>A.git</strong> to a branch in <strong>B.git</strong> by adding <strong>A.git</strong> as a remote on <strong>B.git</strong>. E.g. from <strong>B.git</strong>:</p>
  
  <pre><code>git add remote a_remote [URL to B.git]
  git fetch a_remote
  git merge a_remote/[branch from A.git]
  </code></pre>
  
  <p>As a result I will not get two separate roots in <strong>B.git</strong>.</p>
  
  <p>I just tried to do this on two different repositories of a fairly large size (the two repositories have some files in common) and got tons of conflicts.</p>
  
  <p>If putting aside the best practices discussion here what is actually causing all these conflicts?</p>
  
  <p>And what consequences does it have when a repository have two unrelated roots?</p>