Learn German: Alles war schiefgegangen. - Everything had gone wrong.

The Past Perfect uses the exact same helping verb rules as the standard spoken past tense (Perfekt). Because gehen implies movement or a change of state, schiefgehen takes sein as its helping verb. Therefore, to form the Past Perfect, we use the simple past tense of sein (war) instead of hatte.

How does the word schiefgegangen get put together?

It comes from the separable verb schiefgehen. Schief means "crooked" or "askew," and gehen means "to go." For separable verbs, the past participle prefix -ge- is squeezed right between the separable prefix (schief) and the participle of the main verb (gangen).

Does alles always take a singular verb like war?

Yes. Just like "everything" in English, the German word alles is grammatically singular. Even though it refers to many things, you must use the singular verb war rather than the plural waren.

Could I say Alles war falschgegangen instead?

No, that would sound unnatural. While falsch means "wrong" in the sense of being incorrect, German uses the specific verb schiefgehen (literally: "to go crooked") when talking about plans, situations, or events failing or going awry.