Editor's note: Within 24 hours of US president Donald Trump announcing on Thursday that he would withdraw US troops from Syria, James Mattis resigned as secretary of defense saying he would exit office in February 2019. Beijing News comments:

Some media outlets have attributed Mattis' decision to quit to Trump's announcement to pull out troops from Syria. That's only partly true, for Mattis resigned because of his long-term differences with Trump. Trump's decision to withdraw the troops was only the last straw that broke the camel's back.

Trump and Mattis differed mainly on two aspects: the relationship between the US government and military, and Washington's relations with its allies. For example, Mattis openly opposed Trump's decision to form the US Space Force, saying it would require huge amounts of money, which could be used to meet more pressing needs. He also differed with Trump on sending troops to the US-Mexican border to prevent refugees from entering US territory, although he implemented that decision.

On the second aspect, just as Mattis mentioned in his resignation letter, his "core belief" is that the US' power is "inextricably linked" to its alliances and partnerships with other countries. Which is different from Trump's "America First" policy.

Besides, the fact that Trump announced a successor to Joseph Dunford, chairman of US Joint Chiefs of Staff, nine months before the end of his term shows that the US president's relations with the US military is anything but good. Whether the president can implement his policies smoothly depends on whether the tensions between him and the military ease during the rest of his term.

The Trump administration has seen the resignations of one senior official after another, prompting some media outlets to call it "the administration with the highest demission rate in US history". And since Trump is strong willed and expects his senior officials to share his views and strategies, the resignation of the officials who have basic differences with Trump is only a matter of time.