what is Trade Barrier?请帮忙用英文解释一下什么是贸易壁垒,以及欧美商品是如何打入中国市场的?最好是用英语的?

definition:A government regulation that restricts global trade.

Trade barriers usually are applied in order to meet an economic objective such as protecting domestic industries,reducing unemployment,or preserving foreign exchange,although they may also arise from political disputes among countries or in retaliation for barriers maintained by trading partners.