A Limitless Friendship That Has Boundary Issues: In the runup to Russia’s debacle in Ukraine, China and Russia declared a friendship “without limits.” But both countries know that friendship agreements are fragile things. Less than two decades after China and the Soviet Union signed their last friendship treaty, the two countries engaged in a sharp series of border fights. Expansion-minded Chinese nationalists, coupled with China’s increasing and barely concealed contempt for Russian weakness, have the power to erode Russia and China’s current rapprochement in a matter of moments. The foundations for conflict are deep. China and Russia have bickered and...