Are all Nations on Shortwave radio?

In one word, yes.
However not sll stations are
broadcast stations and many are lower powered and intended for their
domestic audiences. I'm sure that those not having broadcast stations
have "utility" stations such as
military, weather broadcasts, embassies etc. These broacast usually in
USB and many need a decoder to see who is transmitting.
Charlie
Essex, Naryland
Drake R8B EF=SWL antenna