Actually, the phrase "national security" is barely used until the 1930s. And there's a reason. By then, the United States was beginning to become global. Before that the United States had been mostly a regional power - Britain was the biggest global power. After the Second World War, national security is everywhere, because we basically owned the world, so our security is threatened everywhere. Not just on our borders, but everywhere - so you have to have a thousand military bases around the world for "defense."