“The fundamental idea is that owners of capital are going to put that capital at risk for an investment, and they’re going to be asking the question, “What rate of return am I going to get on that investment after I pay taxes?” They’re not curious what their pre-tax rate of return is. They’re curious about their after-tax rate of return.”
While the UK is generally regarded as having a larger military and is certainly understood to have a larger economy from which to finance its military, its advantage on at least some common sense metrics is modest and its demands greater; the UK has more geopolitical interests around the globe to defend. Spain, on the other hand, while somewhat less equipped would have a proximity advantage in any armed conflict over Gibraltar. In short, the winner from such a hypothetical encounter is far from obvious to a casual observer.