War particularly civil war has a terrible cost but is sometimes still necessary.

Rating: 10/10 (27 January 2007)

(No spoilers until after the all caps word "spoilers:" below.) Those writing comments here, and there are many, who say this is an anti-war movie simply didn't understand it. Try watching it again with an open mind.
It is not, any more than Saving Private Ryan is, an anti-war movie. What both movies do is make viscerally and unforgettably real the horrible costs of war. They celebrate the sacrifices of fallen comrades even while they note that sometimes unwise actions on their part, sometimes inept decisions above, and sometimes partly unfathomable altruism was directly responsible.
They are both absolutely at their core movies about not taking a decision to enter war at all lightly. (Which can of course mean they inform a view that wars are often not worth their cost, such as many reasonably feel, the present one in Iraq.) However in both movies the director is plainly and unmistakably saying, for those with any ability to see things outside their own ideological prism, that the wars that each were portraying (WWII and the Korean war) were for their country's and their citizens' well being, unquestionably necessary and worth it.
The title is brilliant and couldn't have been better chosen. In addition to, as I understand it, making reference to the S. Korean national flag, it sums up after you've seen the movie, both the reasons for fighting, and the tragedy of the divided brother nations that resulted.
While S. Korean fanatics both within the army ranks and outside of it are shown as sometimes acting as unnecessarily brutally to civilians as the Communist north, there is no question that the director's overriding message is that fascistic brutality is systematic and pervasive on the Communist side, while more episodic and triggered by rages of revenge for the most part on the Southern one. SPOILERS: The truly lunatic extremes to which the older brother is given once he has crossed over to the N.Korean side in the belief that both his brother and fiancé have been killed by anti-Communist fanatics in the South, is a nice allegory for the then and still now fanaticism of many citizens of the Communist north. His final flipping to fight against the soldiers of the North in his dying moments is clearly an emotional expression of the Southern hope and belief that at some point and somehow their brothers to the North can and will regain their sanity  even many of the lunatic true believers among them.
What this movie clearly does is take the anti-war sentiment that is and especially at the time of the film's release was gripping the young in the South, acknowledges the partial validity of the sentiment, but then moves to show why their fathers were heroes in fighting back against the invading totalitarian North, and why despite the terrible costs it was nonetheless worth it. It's easy to see why it's the most viewed movie in S. Korea ever. It's a moving and fascinating film for non Korean Americans as well. It's an intimate look at people who we see as both similar to us in many essentials, and quite different as well in some others.