Question

Over the last two generations, the united states and most other nations have been __________ tariff rates.

Answer 1

I believe the answer is tariff rates.
Tariff rates refers to the type of additional cost that imposed to a certain product before entering a country.(more tariff rates means that the price of the product will become higher when it enters the market)
Many nations made a lot of effort to lower tariff rates so they could form a mutually beneficial trading relationship with other nations.