Not being boke in this, I googled a little. It seems that Ohr Sameach considered Balfour declaration sufficient for matir nedorim. I wonder whether we have statements on Oaths from other gedolim shortly from pre-state time, without being colored with later history. Any info?
Chofetz Chaim was for political separation from anti-religious Jewish groups in Poland, but I do not see him decreeing against those who went to EY (and he almost went himself, if not his wife’s sickness). Indeed, from his description it seems that anti-religious pressure among Polish Jewry was not different from EY. Seems that some here oppose Zionists more than Bundists or Communists. Not sure, why.