title: Merging two different repositories with different history
body: <p>We end up with 2 different repo with different history as two people started their own repo and now time to merge.</p>
  
  <p>Start code is same and just two different git init and remote.</p>
  
  <p>so condition is Developer D1 started and his repo is:</p>
  
  <p><strong>start-> A->B->C-></strong></p>
  
  <p>Developer D2 started and his repo is:</p>
  
  <p><strong>start->Z->Y->X-></strong></p>
  
  <p>Now, It is desired to have common branch for both repo to pull that they can merge their own branch for new work.</p>
  
  <p>Their work is mostly separate with small conflicts which can be resolve manually.</p>
  
  <p>What command or process should be best?</p>