LONDON • China's recent decision to impose sanctions against two United States defence manufacturers selling weapons and other military equipment to Taiwan is largely symbolic: The two companies in question are hardly likely to seek customers for their products in China, so the sanctions will not have the slightest impact on their future turnover.

Still, the Chinese move is politically significant, for it reaffirms a key international trend: the spread of the use of economic sanctions for political reasons as a key instrument in confrontations between states and, increasingly, as the preferred weapon of coercion.