this
One idea worth considering that wouldn’t hurt and would not change mechanics but would increase visibility of potential problems for newbies would be to change the dialog box of corp invitations/application when the corp in question is at war - make it more visually apparent that the corp is at war (ie. so you don’t have to open up the corp window and read the fine print) so newbies can think twice before joining.
Notice: This corporation is currently at war!
<Brief description of potential implifications>