What is (are) the key competitive advantage of Wal-Mart and to what degree is it sustainable?).

on the Wal-mart case (What are the keys for success in this industry?, What is (are) the key competitive advantage of Wal-Mart and to what degree is it sustainable?). Maximum 1 page per person.https://www.mckinsey.com/business-functions/strategy-and-corporate-finance/our-insights/have-you-tested-your-strategy-lately