China's army is full of underequipped, ill-trained, and undersupplied 2 million soldiers. In a war with the US, most of these soldiers will be useless, unable to attack as they are impossible to transport overseas in any meaningful invasion. Both China's navy and air force, but its air force in particular is very underequipped and outdated. The US and China is separated by a large ocean, which provides huge problems for logistics. If a war does happen, then it will mostly be between aerial and some naval units.
Russia's military too, is inept, which was demonstrated in the Georgian war. Its navy is crumbling, and although its air force is still formidable, it is no match for USAF and the US navy. If a war happens between Russia and the US, then like China, will mostly be limited to air and navy, which will be devastating though. There is also a low chance of the US landing troops at Kamchatka, and an even lower chance of Russian troops landing at Alaska.
All in all, a war is highly unlikely to happen, and even if one happens (excluding nuclear, biological, or chemical wars), it is unlikely to cause damages as much as the ones featured in films