The first return volley in a new trade clash between China and the United States was fired on Monday as Beijing’s tariffs on nearly $14 billion in US imports came into effect.

The US president is dealing with a far more confident China than he did back then. Beijing has expanded its global footprint, and it is now the lead trade partner for more than 120 countries.

China has reiterated its threat to take “necessary countermeasures to defend its legitimate rights and interests” following ...