"China assertively looks out for its own interests on the world stage, as it has done for decades, centuries, millennia."
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I disagree.  They have only become aware of the importance of the world within the past few decades.  Read "The Governance of China" by Xi, and you'll understand their new enlightenment.  China's past was all about keeping the outside world; outside.  The Great Wall was about keeping the world out.  The Opium Wars, were all about keeping the world out.  The embrace of Communism, was all about keeping the world out.
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But things are different today.