but they didn't. why? Because they are the ultimate neutral. Give a good reason for them to do it, the kings of the neutrality.
I interpreted the remark wrong, I read it as "Without them getting attacked after they declare war" not "Declares war without being attacked". About the only thing I can come up with is a US President so vindictive that he makes it clear that he will cut off trade completely from any country that doesn't declare war on Germany during his entire term at least. Not sure even that would work . It is my best shot though.