I have watched an interview where one participant argued that the world is experiencing less and less war compared to what it used to. To emphasize this idea, he said that declaring war is something really rare nowadays and perhaps the last time it happened was between N. Korea and U.S.
I thought of digging a little bit. Not sure, but I think that so-called declaration of war that might have involved N. Korea and the U.S. did not actually happen:
A top North Korean diplomat said on Thursday that the U.S. has “crossed the red line” and declared war against the country by placing the country’s leader Kim Jong Un on a list of sanctioned individuals in connection with alleged human rights abuses in the authoritarian state.
Searching more I could find this article about Chad declaring war ("state of belligerence") on Sudan:
Chad said on Friday a "state of belligerence" existed between itself and Sudan following attacks on an eastern border town by rebels it said were armed and directed by the Sudanese government. While President Idriss Deby's government stopped short of declaring war or breaking ties with Sudan, the statement was the toughest so far against its eastern neighbour over the Dec. 18 attacks against the border town of Adre.
If I understand correctly, there was no actual war declaration here.
A more recent war is the Russo-Ukrainian one, but there does not seem to be any declaration of war here.
When did the last (formal) declaration of war actually occur?