The presidents of China and the United States will meet for an unusual, informal summit in California on June 7-8. Officials on both sides are rightly trying to lower expectations, especially for "deliverables" and detailed outcomes on some of the thorniest issues between the world's top two economies in only two days of personal diplomacy. Instead, they are stressing the opportunity for the two leaders to explore areas of cooperation and reduced competition beyond the short-term calendar.

This summit is the first in more than 40 years when the leaders of two very consequential and different powers will sit down for a "blue sky" discussion. The last was between Chairman Mao Zedong and former US president Richard Nixon in 1972. History has proved the importance of that dialogue for the principles and concepts governing Chinese and American cooperation and competition. Had they bogged themselves down in detailed disputes, which were many, beneficial strategic change would have proved elusive.

The California summit could be similarly consequential for the 21st century. Grinding competition of the sort seen recently between the two countries, potentially leading to conflict, could put them on a path to disaster. Focused cooperation, despite major systemic differences in the structure and interests of the two countries, can lead to more positive outcomes.