Having trained U.S. and foreign troops at Ft. Knox for a number of years, among whom were Saudis and Yemenis, I believe the Yemenis might suffer a massive depopulation should they move against the Saudis.
Ha!
I met a guy here who spent time on the ground with the Saudi armored car brigade as an advisor. Had some interesting stories and (relatively minor) scars involving a Yemeni T-62 I believe it was. The T-62 got the worst side of the bargain.