China and the US lack trust. Neither properly understands the other, what their intentions are or how they see their role in the world. The informal summit between presidents Xi Jinping and Barack Obama at a ranch in California has smoothed some wrinkles, laying a firm foundation on which to build a great-power relationship. Better knowing one another is a good place to start, but now comes the hard part - the meetings at a host of levels that can create confidence and co-operation for mutual and global good.

The summit was that important first step. By breaking with the stiff formality of past Sino-American meetings, the leaders rekindled the spirit of the landmark talks between Mao Zedong and Richard Nixon in 1972 that restored diplomatic relations. The strolls in the tranquil grounds of the Sunnylands estate, a relaxed dinner of lobster and steak and casual conversations were a marked departure from past practice. The unhurried eight hours of get-togethers over two days did not lead to major deals, but that was not the intention: what China and the US most need is to better understand one another.

With their economies so closely interconnected, there is every reason to be on the best of terms. Yet relations have deteriorated to the point that any of a number of tensions could easily escalate to a confrontation. Of most concern for China are Obama's pivot to Asia, a siding with neighbours over territorial disputes and what would seem a closed-door policy to investment by successful firms like Huawei. Americans worry about China's economic and military rise, cybersecurity, intellectual property and the trade imbalance.