“To be successful you need friends and to be very successful you need enemies.” ~ Sidney Sheldon, The Other Side of Midnight. Sheldon’s line is relevant for nations too: To be successful a nation needs friends and to be very successful it needs enemies.
The existence of a formidable enemy serves as a constant reminder to the nation’s political leadership and its population of the fact that there exists an entity that is powerful and dangerous, and if they let their guard down, this entity could devour their nation. Their competition with the formidable enemy fuels their work ethic and geopolitical strategy. They relentlessly strive to strengthen their economy, their political institutions, and their military to match the strength of their enemy and, if possible, surpass it.
If a formidable enemy does not exist, then a nation must invent it.