The country’s five largest health insurers are now down to three, or will be, if state and federal regulators allow the deal to go through. Aetna (NYSE:AET) bought Humana (NYSE:HUM) for $37 billion of cash and stock, which gives Aetna a larger slice of the growing Medicare Advantage market. Anthem (NYSE:ANTM) bought Cigna (NYSE:CI) for $54 billion, which would create the country’s largest insurer by individuals covered, as well as Cigna’s higher-margin large employer plans and overseas business. Whether regulators will approve the deal is critical to investment strategy, and I honestly have no idea which way regulators will go. Their decision will depend on the fundamental structure of the healthcare market under the Affordable Care Act. Let’s look at the industry first, then look at specific investment options.