What is one cause for this failure?
Resource tags defined in the CloudFormation template are specific to the us-east-1 Region.
The Amazon Machine Image (AMI) ID referenced in the CloudFormation template could not be found in the us-west-2 Region.
The cfn-init script did not run during resource provisioning in the us-west-2 Region.
The IAM user was not created in the specified Region.
Explanations:
Resource tags are global across regions and do not cause issues when launching resources in different regions. Therefore, tags are not the cause of the failure.
AMI IDs are region-specific. If the AMI ID referenced in the CloudFormation template does not exist in the us-west-2 region, the EC2 instance cannot be created.
The cfn-init script is executed during the EC2 instance initialization but is not the primary cause for failure of creating an instance across regions.
IAM users are not region-specific; they are global. Therefore, the region in which the user is created does not affect CloudFormation stack deployment.
I figure that the answer is:
The Amazon Machine Image (AMI) ID referenced in the CloudFormation template could not be found in the us-west-2 Region.