Amid warnings of price increases, Canada moved quickly to retaliate, China said it had planned countermeasures and Mexico said it would soon unveil its response.

President Donald Trump is taking a blowtorch to the rules that have governed world trade for decades. The “reciprocal’’ tariffs that he announced Thursday are likely to create chaos for global businesses and conflict with America’s allies and adversaries alike.

With less than a month in office, the president has pursued trade actions that could shatter the global trading system and dwarf the trade measures he took over his entire first term.