For reasons that do not involve US military might, attacking a nation that did nothing wrong is political suicide and could anger people into going insurgent as doing so is a massive red flag that their own government has become irrecoverably corrupt, thus starting a civil war in the attacking nation.
Keep in mind this varies by nation:
Canada is a good candidate for a civil war over an extremely questionable military conflict because it's a western nation that has not become overtly totalitarian, and the fact that America could easily crush Canada would likely amplify it.
China may not have a civil war without smuggling weapons to dissidents because of said nation's totalitarian nature, but the war will still cause some problems in China as it's unpopularity would cause a small trickle of people to flee, which will amplify quickly if US troops were to ever touch down on PRC soil. China also has multiple candidates in regards to arming insurgents, such as the Tibetans, non Islamic Uighurs, and all the regular Mainland and Hong Kong dissidents.
Honestly, if people want in on WW3, we got that covered. GEOTUS has shown he will bomb your ass if you mess with him.
See Iran.
For reasons that do not involve US military might, attacking a nation that did nothing wrong is political suicide and could anger people into going insurgent as doing so is a massive red flag that their own government has become irrecoverably corrupt, thus starting a civil war in the attacking nation.
Keep in mind this varies by nation:
Canada is a good candidate for a civil war over an extremely questionable military conflict because it's a western nation that has not become overtly totalitarian, and the fact that America could easily crush Canada would likely amplify it.
China may not have a civil war without smuggling weapons to dissidents because of said nation's totalitarian nature, but the war will still cause some problems in China as it's unpopularity would cause a small trickle of people to flee, which will amplify quickly if US troops were to ever touch down on PRC soil. China also has multiple candidates in regards to arming insurgents, such as the Tibetans, non Islamic Uighurs, and all the regular Mainland and Hong Kong dissidents.