Mirror a folder erases all on target drive

[pjm]

I mirrored a folder from my windows 10 c drive to my seagate external drive. After the copy, the earlier backups had been deleted.
Maybe I cocked up as it was my first day using 'FreefileSync. But stil a worrying event.

[Plerry]

If you run a Mirror sync variant, after the sync the content of your right (target) location will be identical to that of your left (source) location. So, everything that was in your right location, but is not (or no more) in your left location, will be deleted from your right location.
This is the very nature of a Mirror sync.
If that does not suit your needs, you may consider to use the Update sync variant.
This Update variant will make sure that everything present in your left-side location will be in your right side location, but will not delete anything preexisting in your right side location.

[pjm]

Thanks for the helpful reply.
My apologies for the unintentional double post.