Legally, absolutely. If the US declared war on all of Europe tomorrow, there's no meaningful question what Google would do.

... but practically and on the ground, the Google employee base is large and international enough that there may very well be employees with friends or relatives in US military hot-zones where the US has not successfully demonstrated sufficient care about civilian casualties. Their desire to only work for the company in relatively peaceful times is pretty understandable.

Nobody wants to wake up one morning and realize they're an IBM employee in 1940.