The back and forth tariff impositions between China and US are sparking off major tensions. But what is the purpose of tariffs, and why have nations imposed them? Jim Spellman takes a look into the driving force behind the measure.

US trade barriers are not a new phenomenon. Over the years, they've been used especially when economic times were tough. For example, the 1930 Smoot-Hawley Tariff Act was signed into law in response to the Great Depression. It raised import duties to protect U.S. businesses.

Fifty years later, as the U.S. auto industry faltered, import quotas were imposed on Japanese cars.

But as President Donald Trump embraces a potential trade war, the U.S. economy is doing well- with low employment and a booming stock market. Many analysts say the ongoing trade dispute may have more to do with politics than the economy.

PAOLO VON SCHIRACH GLOBAL POLICY INSTITUTE "Why now? Why all this? Why are we on a war footing? Because perhaps he fears, Mister Trump and his political advisers, fear that he may be losing the grip on the people who voted for him, and he's thinking about the mid-term elections and maybe already gearing up for the next presidential election, and he wants to consolidate his base by showing the toughness that put him in the spotlight to begin with."

Trump began his run for office promising to take on China.

DONALD TRUMP US PRESIDENT "When was the last time anybody saw us beating, let's say, China in a trade deal? They kill us. I beat China all the time, all the time."

Trump's tariffs are designed to help U.S. workers in rural areas and the industrial Midwest -- his political base. But China's countermeasures are also aimed at those same areas.

ENZIO VON PFEIL ECONOMIST "Trump is seeking to appeal to people in Wisconsin, Wyoming, Montana, states like that, that frankly don't have a lot of contact with the foreign world except through exports of soybeans and pork. And that's where the Chinese will come in big time trying to target those industries."

China has made clear that it will not back down from a trade war.

WANG SHOUWEN CHINESE COMMERCE MINISTER "China does not want a trade war, because there will be no winner in a trade war. If someone insists on starting a trade war, China will fight till the end."

Which means the impact on the U.S. economy could get worse and Trump's political gamble could backfire.

SARUHAN HATIPOGLU CEO, BERI "If you are sacrificing your economic benefits or the welfare of your nation for political gain, when those individuals be it agriculture or manufacture start getting hurt because of these policies, the patriotism is not going to work. At that point, President Trump might not find a big enough American flag to hide under, because he'll lose that election."

JIM SPELLMAN WASHINGTON "Many economists say avoiding a full blown trade war makes the most economic sense for both the U.S. and China, but politics may be a bigger driving force than sound economic principles. Jim Spellman, CGTN, Washington."