Tariff WatchCountry of origin decides which trade remedies reach a shipment. It is a legal determination about where the goods were produced, not a record of the route they traveled or where the seller is established.
Substantial transformation
A new article, with a new name, character or use.
For most purposes the origin of goods produced in more than one country is the last country in which they were substantially transformed: worked on to the point that a new and different article of commerce emerged, with a name, character or use distinct from what went in. Assembly of finished components generally does not meet the test; a change that alters what the article is generally does.
Trade agreements apply their own rules of origin instead, which are set out in the agreement and in the general notes to the schedule. Those rules can turn on a change in tariff classification, on a regional value content threshold, or on both, and a good can be of one origin for marking and another for preference.
Why it decides the duty
Remedies are scoped by origin, not by shipment.
A Section 301 duty on goods of China reaches goods of Chinese origin wherever they are shipped from. Transhipment through a third country does not change origin, and a declaration that it does is a false statement on the entry.
Origin is also what a country-wide action turns on. Where an action reaches all goods of an economy, the classification is irrelevant to whether it applies and the origin is the whole question.
Related
Elsewhere on this site.