To understand this sentence it's necessary to know from context that Manassas refers to an event, specifically, the first major battle of the American Civil War. The article cited does make this clear if you keep reading, but the headline is sloppy for a learning-English site — it should not assume that readers already know this. (A newspaper with a primarily-American audience can assume readers already know this, and that's probably why the mistake was made.)
Because "Manassas" is an event, the next word, "ends", should be understood as the main verb of the sentence, and it should be understood in the sense "causes the end of". "Hope for a short war" is the direct object, the thing whose end was caused.
A less terse version:
[The [first] battle of] Manassas ended hope [by the general public] for a short war [sp. the American Civil War].
(recast in the past tense because I am no longer describing this event as if it were current news)
(Manassas is also the name of a place, and the battle has that name because it occurred close to that place. However, the Civil War is covered in detail in US history courses and still has immense influence on our collective imaginations, so "Manassas" without qualification or context refers only to the battle. Adult native speakers of American English who don't live in that area would generally say "the city of Manassas" or "Manassas, Virginia" if they meant the place.)