Current trade frictions between China and the U-S have been going on since the Trump administration slapped heavy tariffs on Chinese goods based on the Section 301 investigation. CGTN's Timothy Ulrich has more.

The US has opened six 301 investigations against China, spanning more than two decades. All of the actions ended in agreements settled through negotiations.

Case in point, the US initiated an intellectual property investigation against China in April 1991. The US announced a preliminary retaliation list including China's garment exports to the US, sports shoes, and electronics--with a 100 percent tariff – totalling 2.8 billion US dollars. The two countries then signed an Intellectual Property protection agreement the January after and China promised to improve its IP laws.

In October 1991, the US conducted a 301 investigation against China again, which they said was because US products encountered unfair barriers-of-entry into China. The US then announced a retaliation list worth 3.9 billion US dollars. The disputes ended with China promising to lift import barriers on US products for five years.

The US initiated two more intellectual property investigations against China in 1994 and 1996. Both ended with IP protection agreements between the two countries.

After China entered the World Trade Organization, the Obama administration announced another investigation against China. The US conducted an investigation on a series of clean energy policies. However, the investigation did not result in any sanctions. The two countries negotiated under a WTO dispute-settlement mechanism, and China eventually agreed to modify relating terms.

The latest 301 investigation against China was launched in August 2017, and targeted intellectual property. At the beginning of April 2018, US Trade Representative Robert Lighthizer announced that the US would release a list of some 1,300 products that were liable to a 25 percent tariff – worth a total of 50 billion US dollars.

Beijing retaliated by publishing a list of US imports--also worth 50 billion US dollars and levied a 25 percent tariff. China's hit list was smaller, but carefully targeted to hurt sensitive US sectors, such as soybean farming.

Timothy Ulrich, CGTN.