Why do nations withdraw embassies when they declare war/war is on the close, close horizon?
Just my WAG, but I can think of at least three reasons:
It’s ancient tradition, dating back hundreds - if not thousands - of years.
It’s to prevent the embassy staff from being arrested as spies, or even killed outright. After all, they’re the enemy now.
It’s a philosophical thing: it’s saying, “Talk’s done. Now we fight.” After all, if the two nations were still on speaking terms they wouldn’t be at war, would they?
I’d add to this that the documents stored at the embassy would be valuable to the hosting country. Better to pack things up and head home rather than leave sensitive documents lying around for the enemy to capture.