In the months leading up to Xi Jinping making common cause with Russian President Vladimir Putin, the Chinese leader was focused on one country, and it wasn’t Ukraine.

His ambitions for alignment with Mr. Putin had one main purpose: presenting a united front against the U.S. The result, according to Chinese officials, foreign-policy advisers to Beijing and an analysis of public statements, was the Feb. 4 China-Russia declaration that the countries’ friendship had “no limits.”