The psychology of patriotism, dying for one's own country
The quote "Dulce et decorum est pro patria mori" is from one of Horace's Odes (III.2.13), and it translates as: "it is sweet and honorable to die for one's fatherland".

It is assumed that Horace did not glorify the death of a soldier in this poem but allude to the two predominant philosophical doctrines of his time, epicureism and stoa, and their perspective on the summum bonum, the greatest good. For epicureism this is lust ("sweet" in the quote), for the stoa it is virtue ("honorable").

From Horace's point of view, dying for your home country contradicts neither the epicureic nor the stoic ideal, as it implies both. Both philosophical doctrines were sceptical of a service to the state, and Horace says that serving your country is in tune with both doctrines.

Death for your country is glorified in a quote from Horace's Greek source, a verse by Tyrtaios  (Fragment 6D) about the service of the Spartans:

"The most beautiful death of all is when a warrior fights for his fatherland and dies for it."



Source:

Common internet knowledge ;-)