This may be obvious to others, but it wasn't to me.
I was setting up Terraform remote state storage (to an s3 bucket) like so:
terraform remote config -backend=s3 \ -backend-config="bucket=mig5-terraform-state" \ -backend-config="key=terraform.tfstate"
I kept getting the error on the above:
Failed to read state: Error initializing remote driver 's3': missing 'region' configuration or AWS_DEFAULT_REGION environment variable
This worked, of course: