This is a very broad question and there are many important factors that need to be considered. In light of this, let me offer a number of important points worth considering.
- The Trojan war took place between the Greeks and Trojan in what is now known as the country of Turkey. However, it took place so long ago that very little in known. Our best source is still the epic poems of Homer - the Iliad and Odyssey.
- In light of this point, we need to be critical in terms of what really happened. Unfortunately, we are in the dark and things probably will not change. With that said, there are some general points that we can say with near certainty. First, the Greeks defeated the Trojans. Second, this war are "huge" in the memory of the ancients. Third, this war defined ideals in the ancient world, even to the time of the Romans.
- If we look at the poems of Homer, the chief characters were Agamemnon and Achilles. They hated each other, but they worked together. Agamemnon needed the greatest hero among the Greeks and Achilles sought glory and honor.
- If we can trust the Roman poet, Virgil, then the Romans came from Troy through Aeneas. Again we need to careful from a historical point of view.
In the end, we can say that while details of the Trojan war are lost in history. However, this war shaped the mind of the West in many ways through the poems of Homer.
Many of the details of the Trojan War are greatly obscured, due to the fact that there are not many factual documents found. (most are literature pieces which tend to be created for entertainment value rather than a factual value.)
However there is definite solid proof that the city of Troy existed, and that there was a series of conflicts which resulted in the destruction of Troy.
The more common explanation as to why there was a Trojan War was because Paris, a prince of Troy that was cast out as a baby, was chosen as a judge to say who the most beautiful goddess was. Each goddess offered a different bribe, and paris chose Aphrodite's, which was the love of the most beautiful woman in the world. Paris was re-discovered as a prince, and sent on a diplomatic mission to Greece, where he met and fell in love with Helen, and kidnapped her. The Greeks, who had all fought over Helen, had agreed to support whoever she married, so they united to take her back.
However the more likely reason, is that the Greeks saw Troy as a rich place to loot and conquer.
As for the events. Again greatly obscured. But the story goes that the Greeks laid siege to Troy for many decades and were completely unable to pass the Trojan defences, and created a wooden horse tricking the Trojans, and resulting in the destruction of Troy. We know for sure that this is a myth.
The outcome: Troy was destroyed. A Trojan Commander Aeneas, fled Troy with his family, and founded a new city called Rome. This is again highly debatable.