With trade hostilities between the world's two economic superpowers back on, China has sent the unmistakable message that it is ready to fight. A week ago, it invoked its grip over virtually the entire world's supply of critical materials, breaking a delicate trade detente between the two countries. Beijing feels it has another ace card: its booming factories. Even in the face of sky-high tariffs by President Donald Trump, China's manufacturing sector is helping to maintain growth and give the country's top leader, Xi Jinping, a stronger hand to face down the United States. The strength is on display in the city of Yiwu, home of the world's biggest wholesale market, where sellers peddling toys, home electronics and drones are stuffed into complexes that span multiple city blocks.