The configuration history uses CIs to retain a complete history of the events of each resource that AWS Config monitors over a given period of time. This allows you to check the status and configuration of any resource from any point.  This configuration history can be queried programmatically or by using the AWS Management Console where it displays the history within a visual timeline of events as shown with this VPC:

To use the AWS CLI, you would use the following API:

aws configservice get-resource-config-history

This API could be used with the additional parameter to drill down to specific resources and resources types, such as an EC2 instance:

aws configservice get-resource-config-history --resource-type AWS::EC@::Instance --resource-id i-0ba7aa7ccbc805b45

All of the configuration history files are stored in a predefined S3 bucket selected during the configuration, for high availability of the data. Each configuration history file only contains the CIs for a particular resource type over a given period of time; for example, a configuration history file might show all changes to EBS volumes over a period of six hours.