A shipping
war is when two or more
people have an argument over a paring of most likely fictional characters. Often fan art of the ship that lets say, person A likes will be sent to person B to upset them and vis versa. Shipping wars are either to prove the others ship wrong, to get the person to abandon their ship, to start shipping the pair you do, or simply to anger someone. Usually each person will bring up cannon situations and parts of the movie/book/show/manga/
anime/etc to either back up why they ship that pairing or to prove why the other ship is irrelevant. Shipping wars can be
long and tedious especially if a large group is involved. If someone's
OTP is involved the
war will most likely be longer and will be more like a flame
war. If the same character is involved but each person ships them with a different character the
war will be more hate filled and canon will be used a lot. If your ship has liittle to no canon backing it up you will most likely loose. Canon is an essential in a shipping
war.
Let's say two
people in the Attack on Titan
fandom had a shipping
warPerson A shipped Levi x Eren but Person B shipped Levi x Hanji. Because the character Levi is in both ships, conflict will arise. Person B would be at a canon advantage because there is more of a
history and friendship with the characters. They could all so bring up canon examples of when the characters Levi Eren didn't get along. And if all fails bring in the factor of age, Eren only 15 while Levi is 34. Person A won't have really any canon to back them up so the best they could do is resort to fanart to either annoy or get Person B to at least understand their ship.