ZSK, I think for RJBS, RZ is very much related to MO – as in Orthodoxy is modern and is addressing modern issues, of which Israel is a major one.
Someone forwarded RJBS a newspaper article during WW2, asking him to respond in the paper. The article was by a British Jew who was astonished to observe German Jews in British internment camps. They were sitting and learning Gemora without paying attention to events around them. He writes – how can they be so focussed on discussing wars of the Roman Empire while totally ignore Normandy operation that may affect their whole lives. Are we a nation that is capable to operate in today’s world?
Rav did not respond to this letter at the time, but mentioned it 10 years later during heated discussions in Israeli Knesset: if the author of that article is still alive, he can now see Jews addressing issues of the day.