A company currently deploys infrastructure in one AWS Region and wants to define the infrastructure as code with plans to expand to multiple Regions and multiple AWS accounts. What approach should the solutions architect use to manage and deploy the infrastructure across accounts and Regions?

The correct approach is to use AWS Organizations with AWS CloudFormation StackSets. AWS Organizations allows you to centrally manage multiple AWS accounts, while CloudFormation StackSets enable you to deploy, update, or delete CloudFormation stacks across multiple accounts and Regions with a single operation. This provides a scalable and efficient way to manage infrastructure as code across a multi-account, multi-Region environment. The deployment should originate from an account with the necessary IAM permissions, often a delegated administrator account within AWS Organizations. Using only CloudFormation templates with IAM policies is less efficient for multi-account, multi-Region deployments as it requires individual deployments or complex scripting. AWS Control Tower is for setting up and governing a multi-account environment but doesn't directly deploy infrastructure as code across accounts and Regions in the same way StackSets do. Nested CloudFormation stacks are for organizing resources within a single stack, not for deploying across different Regions or accounts.