The days of invasions are long gone, instead what you have is annexation actions like what Russia did with Crimea. Lots of people in Crimea are ethnically Russi

The days of invasions are long gone, instead what you have is annexation actions like what Russia did with Crimea. Lots of people in Crimea are ethnically Russian, and they were tired of Ukrainian rule, so they sat by and let the Russians take over. Militaries don't really prevent invasions. Border security is about more than just securing from outside belligerence. It also does things like keeping fishermen from fishing in your waters, drug cartels from operating freely, and the like.