“Patriotism is your conviction that your country is superior to all others because you were born in it”. (George Bernard Shaw)
Maybe, but there is nothing wrong with that – it is human and part of our tribal make-up. What is bad news is nationalism, which is the aggressive face of patriotism, based on ignorance and a reluctance to understand the cultures and point of view of other countries (as in, “we can have nuclear devices because our country is morally superior to yours; you can’t because you are a bunch of towelheads”). It is also used by politicians to justify war, whip up hysteria and exploit mankind’s worst instincts. Hitler was the prime example, but there are many others.
Nationalism as such didn’t exist in the time of Epicurus, but intense competition and petty warfare between city states certainly did, and Epicurus deplored it. Talk and negotiation is the better way. (Yes, pretty obvious! But I want to make the distinction between gentle pride of country and jingoism).
It is said that economics were behind the outbreak of the First World War. But its obvious manifestation was nationalism, particularly stoked by the Kaiser and his militarists, along with the roiling nationalisms of the Balkans, indeed, most of Europe to a greater or lesser degree. This is why the EU, despite its stupidities and bureaucracy, is so important. The people who run it down or want to leave it are a menace to future generations.
“Nations” came into being in the first instance to claim loyalty in return for providing security for its people. It is when nations shift instead to beating up on other “nations” to create empires that death and destruction follow. Epicurus lived at a time of imperial struggles but even if he couldn’t escape it he at least enjoyed the good fortune of owning a garden where he could ignore all that.