As US President has started work in full swing, many Chinese leaders believe that, now a war with America maybe a practical reality. US President has moved away from a decades old one China policy that the US followed, by speaking to the democratically elected leader of Taiwan, Tsai Ing Wen. China believes that Taiwan is a part of its territory, but it practically does not control it. Taiwan has a separate military, economy and a democracy.
The recognition given to it by the USA has caused a lot of heartburn amongst mainland Chinese people. US President has for long called China a currency manipulator that has hurt many US businesses as they lose business to cheap Chinese imports. No US President has made such comments, so bluntly. China has also been accused of illegally occupying islands in the South China Sea.
Current Secretary of State Rex Tillerson has said that they would not shy away from blocking China from these islands, by using US Navy ships. China has said that it would consider such behaviour as an act of war. It is for these reasons that China says that it feels war with USA is now a practical reality.