[danbruc]

If security is guaranteed by nukes, why does the US threaten the Salomon Island? Placing missile defense systems close to the launch sites gives you the possibility to intercept them early in the boost phase when they are still slow. Having assets close to enemy borders in general gives you shorter reaction times. This is about tipping the scale somewhat in your favor, not ensuring your victory.

I am not qualified to judge the situation with Finnland, but not all neighbors are necessarily equal. Things like geography, for example, might play a role and Finnland in, Ukraine out might be more desirable than Ukraine in, Finnland out.