It doesn't really matter what campus it says you'll be in, but the War Studies Dept is based in Strand Campus and most of the classes will be there- even if you have a few on Waterloo Campus it only takes 5 mins to walk from Strand. I'm not sure why it says Waterloo but I really wouldn't worry about it. Could be admin related, or perhaps the course convenor's office is is over there so they just assign it to all of their students.
I went to KCL for undergrad and got my offer for ICS five days ago too, but I can't find my offer letter or the 'your offer' tab in the menu at all. Did you have any difficulties finding it or was it right there on the homepage or next to the new application and help tabs? I've given it a few days to see if the system needed to update but now I'm not sure if I'm being an idiot or if I'm gonna need to send an email to access it. Thanks!