Learn German: Die Verstärkung wurde angefordert, weil sich der Waldbrand schnell ausbreitete. - Reinforcements were requested because the forest fire was spreading quickly.

In German subordinate clauses, if the subject is a full noun like der Waldbrand rather than a pronoun, object pronouns like sich usually come right after the conjunction (weil). If the subject were a pronoun, it would come first, for example: weil es sich schnell ausbreitete.

Why do we use a reflexive verb (sich ausbreiten) for a fire spreading?

In English, the verb spread can be used intransitively (without an object). In German, ausbreiten usually needs an object. When a physical phenomenon like a fire spreads on its own, it is conceptually spreading itself, so German requires the reflexive form sich ausbreiten.

Why is the prefix aus attached to breitete if ausbreiten is a separable verb?

While ausbreiten is a separable verb, the conjunction weil creates a subordinate clause, which pushes the conjugated verb to the very end of the sentence. When a separable verb is pushed to the end, its conjugated stem and prefix reunite and are written together as a single word: ausbreitete.

How is the passive voice constructed in the phrase wurde angefordert?

This is the action passive (Vorgangspassiv) in the simple past tense (Präteritum). It is built using the simple past form of the helper verb werden (which is wurde) along with the past participle of the main verb (angefordert). It focuses on the action taking place rather than a finished state.