Avram in MD: the obtuseness remark was not addressed to you.Sam2 characterized me so. But allow me to deal with your main remark.
The Rambam absolutely allows a war to defend oneself a milchemes mitzvah (see sefer melochim 5-1) so you are correct in your assumption. I am not sure how the crowd who espouses the sholosh shevuos would deal with this. Does that mean that they would have fought against the Germans YM”S but not against the Arab armies? I don’t know. The sad irony of their approach would be that you could fight your enemies in chutz Lo-orets (like in the megillah) but not in Eretz Yisroel. What corruption of this maamar chazal!