Final answer:
Customs area members, mainly industrialized countries, have significantly reduced their tariff rates against the outside world over the past 60 years, with average tariffs falling from 40% in 1946 to less than 5% by 1990 due to GATT negotiations and WTO efforts.
Step-by-step explanation:
The general trend regarding tariff rates against the outside world among customs area members, specifically industrialized countries, has been towards lower barriers to trade. Historically, as evidenced by the period from 1946 to the end of the 20th century, tariffs have notably decreased. The average level of tariffs on imported goods was as high as 40% in 1946, but after many rounds of GATT negotiations and the continued work of the WTO, this was reduced to less than 5% by 1990. U.S. tariffs followed this trend as well, which shows a significant drop from high rates during the Great Depression to less than 2% by the century's end. This reduction was so considerable that the focus of trade negotiations shifted from just tariff reduction to a broader range of trade barriers, including import quotas and nontariff barriers, which also have been generally lowering over time.