When China's president, Xi Jinping, visited Manchester in October 2015, there followed a bizarre photo opportunity and a bold statement. The former was an image of two global leaders - Xi and then UK Prime Minister David Cameron - posing alongside Manchester City striker Sergio Aguero. The unlikely selfie went viral on social media. The latter laid out a target that seemed much more likely for a nation of 1.4 billion people - and the football world took notice.