First thing, people need to find out, who owns the country, who rules the country. As Karl Marx once said, The working men have no country, In most of the cases, today the country is ruled and owned by the very few, they take most of the benefits, profits while the majority are nothing more than wage-slave, just like you can't say Spartacus uprising is a betrayal to Rome, Rome whether it's powerful and not, has nothing to do with the slave, similar applies to today's bourgeois state.
In today's world, capitalists always use the 'Nationalism' and ‘Patriotism’ to guide the workers to fight with workers of another nation, to divert the attention of class struggles, this kind of nationalism and patriotism is evil, is shameful. A common way of doing so is by invading another country, putting the soldiers, the workers to think that it's an honor to for his nation to kill their 'enemy', like Adolf Hitler had done once, however most of the time the soldiers are the one just dies on the frontline while those rich and powerful people just enjoy their life back in the city.
However, if you were invaded by Nazi Germany or Japanese fascists or American imperialists, there's no wrong in patriotism since you are defending the freedom and independence of your nation.
Basically, anyone who thinks it's necessary to invade or sabotage another country in order to benefit his own nation is bad and evil. If someone just defending his nation's freedom and independence, its good. Nationalism usually involves the previous one, starting wars against other nations while patriotism can be the latter, but not 100% true in some cases, like Nazi soldier defending Hitler is definitely not patriotism.