Answer the following question: Given the following passage  "The brewing industry is a global business, consisting of several dominant multinational companies and many thousands of smaller producers ranging from brewpubs to regional breweries. More than 133 billion litres (35 billion gallons) are sold per year—producing total global revenues of $294.5 billion (£147.7 billion) in 2006. The history of breweries has been one of absorbing smaller breweries in order to ensure economy of scale. In 2002 South African Breweries bought the North American Miller Brewing Company to found SABMiller, becoming the second largest brewery, after North American Anheuser-Bush. In 2004 the Belgian Interbrew was the third largest brewery by volume and the Brazilian AmBev was the fifth largest. They merged into InBev, becoming the largest brewery. In 2007, SABMiller surpassed InBev and Anheuser-Bush when it acquired Royal Grolsch, brewer of Dutch premium beer brand Grolsch in 2007. In 2008, InBev (the second-largest) bought Anheuser-Busch (the third largest), the new Anheuser-Busch InBev company became again the largest brewer in the world. As of 2015[update] AB InBev is the largest brewery, with SABMiller second, and Heineken International third.",  answer the following question. Note that the answer is present within the text.  Question: What economic principle has led to the success of brewing companies in the brewing industry?
Answer:
economy of scale