On Wednesday, Russian President Vladimir Putin met with Chinese leader Xi Jinping in Moscow to deepen their alliance as they face political and economic pressure from the U.S. administration under Donald Trump.

During the meeting, Jinping called Putin his "best and bosom friend" and said that "We treat each other with respect, candor, understanding and trust," CNBC reported.

One major reason why the two countries are so close to each other is that they both have a tense relationship with the United States. U.S. President Trump has slapped tariffs of 25% on $200B of Chinese goods imported to the U.S., which has hurt the Chinese economy. The United States has also put Chinese phone manufacturer and telecommunications company Huawei on a blacklist.

Russia has been facing criticism due to its alleged interference in the 2016 U.S. Presidential election. Russian positions have also clashed with American views on foreign policy. Russia supports Venezuelan President Nicolas Maduro, who the United States would like to see deposed. It also supports the Iranian and Syrian governments which have fraught ties with the U.S. The U.S. government has also continued sanctions on Russia due to its annexation of the Crimean Penninsula in the Ukraine.

The two countries share a strong economic relationship with $108B of trade between them in the last year. The two countries share cooperation in not only economic terms, but also in regards to their political goals.

"For now, what binds them together is common cause against U.S. global leadership, their shared interest in political survival, their similarly autocratic systems and the personal closeness that has grown between leaders who have acted to concentrate more power in their own hands," Frederick Kempe, the CEO of the Washington, D.C.-based think tank The Atlantic Council, wrote about the Russian-Chinese relationship. "The result is closer cooperation across areas from space navigation and technological development to global diplomacy and intelligence gathering."

On Thursday, Xi and Putin will attend the annual St. Petersburg Annual Economic Forum, "a global platform for members of the business community to meet and discuss key economic issues facing Russia, emerging markets and the world as a whole," its website says. Jon Huntsman, the United States ambassador to Russia, is boycotting the event due to the Russian arrest of American private equity manager Michael Calvey.