I know this is gonna be controversal but technically speaking, there are no Russo-Ukrainian War, but Russo-Ukrainian Conflict since Russia did not declare war on Ukraine.
It has a scale of a war but it is not officially a war yet.
It has a scale of a war but it is not officially a war yet.
The US has not declared war since World War 2.
The past 20 or so years of conflicts in Iraq, Afghanistan, and other places was officially "Authorization for the Use of Military Force" [1], not a war. (Notwithstanding the frequent use of the term "war on terror".)
Under the US Constitution, war declarations are typically made against opposing nation-states and are performed by the US Congress [2].
[1] https://en.wikipedia.org/wiki/Authorization_for_Use_of_Milit...