alt Hacker NewsIt's not just the US, very few wars have been formally declared after WW2, because we all learned war is bad™, so we added more and more rules (both international and national) to make it harder to do it.
But the reasons wars existed didn't go away, so this just resulted in more and more people getting killed in "special military operations" or similar things. See e.g. "Why States No Longer Declare War"[0].
[0] https://www.researchgate.net/publication/228896825_Why_State...
That article says that nowadays countries no longer declare war, because now there are a lot of international treaties that restrict what may be done during wars.
Not declaring war provides a workaround, allowing the states to do whatever they desire, without constraints, while avoiding being accused that they do not observe their obligations assumed internationally.
Seems plausible.