Final answer:
Over the last 60 years, trade barriers, including tariffs and nontariff barriers, have generally trended lower, particularly after several rounds of GATT negotiations leading to significant reductions.
Step-by-step explanation:
The general trend of trade barriers over recent decades has been towards becoming lower. After the Great Depression, where tariffs had increased, a dramatic decline in trade barriers was observed, especially following decades of negotiations through the General Agreement on Tariffs and Trade (GATT).
For instance, the average level of tariffs on imports charged by industrialized countries reduced from 40% in 1946 to less than 5% by 1990. Similarly, U.S. tariffs followed this pattern, decreasing to less than 2% by the end of the century. Even though measures for import quotas and nontariff barriers are less precise, it's acknowledged that these have generally decreased as well.