Homer certainly has dual feelings about war. On the one hand, Homer's opinion about war conforms with the traditional opinion of war held by the Ancient Greeks, an opinion that really was not shaken until the world experienced World War I--that to fight and win in war is an honor or glorious. However, Homer certainly also shows that he does not approve of the causes of war, such as rage. What's more, Homer even shows that there are other honors that are far more important than the honor of war, such as the manner in which we treat our own people. Hence, all in all, Homer is showing that while war can be glorious, war is also detestable in so much as war can be caused by, and is most often caused by, rage.
We especially see Homer's opinion that war can bring honor and glory in parts where the poet talks about the honor individuals will bring to themselves and their people through winning the war as a show of valor and self-sacrifice, which is in keeping with classic Ancient Greek thought concerning war. Books IV and V of the Iliad bring a whole lot of conflict and quarrels among the Achaeans as they decide what to do without Achilles. At one point in Book IV, King Agamemnon scolds Diomedes, son of the king of Argos, often spelled Diomed, for hiding by his chariot and looking cowardly. When a friend of Diomedes tries to belittle Agamemnon's insult, Diomedes reminds him and the readers of the importance and honor of war, saying:
Hold your peace, my friend, as I bid you. It is not amiss that Agamemnon should urge the Achaeans forward, for the glory will be his if we take the city, and his the shame if we are vanquished. Therefore, let us acquit ourselves with valour. (Bk. IV)
Diomedes' philosophy about the honor and shame concerning war is certainly in keeping with Ancient Greek thought in that the Ancient Greeks viewed heroes as those who are brave, able to sacrifice themselves for the greater good, and who gain honor through their successes. Hence, as an Ancient Greek, Homer would agree with the general philosophy that success through war due to the valor and self-sacrifice that war requires certainly brings honor, and war in and of itself is honorable. However, Homer also certainly sees that particular causes of war are very dishonorable.
Homer certainly makes it very clear in even the very first book that one of the causes of war is rage, a cause that he sees as being very dishonorable. First, the whole Trojan war was caused by the rage King Menelaus felt at having Paris, Prince of Troy, take from him his wife Helen, a rage, which, actually is understandable considering that Menelaus was dishonored. Secondly, King Agamemnon, leading the Achaeans, insults Achilles by taking away his war prize, causing Achilles' rage--the rage the entire poem is centered around. This rage incites Achilles, the Achaeans most powerful fighter, to abandon the war, leading to all kinds of tragic deaths. Based on the opening lines of the poem, we can see very clearly that Homer finds rage dishonorable and finds it to be a very dishonorable cause of both war and other strife. What's more, since so much death and destruction centers around the fact that Agamemnon needlessly dishonors Achilles through taking his war prize, we see that Homer is also asserting that there are other honors that are greater than the honor that comes from war, such as the honor which comes from treating your fellow human beings in an honorable and respectful way.