Learn Dutch: Omdat de koning vluchtte, werd de stad door het leger veroverd. - Because the king fled, the city was conquered by the army.

We use werd (the simple past singular of the auxiliary verb worden) and the past participle veroverd. In Dutch, a past action that was done to the subject uses the past tense of worden, unlike English which uses the past tense of the verb to be (was).

Why does the second half of the sentence start with werd de stad instead of de stad werd?

This is because of inversion. The entire first clause (Omdat de koning vluchtte) acts as the first block of information. Because the Dutch main verb always wants to be in the second position, werd comes immediately after the comma, bumping the subject de stad to the third position.

How do we say "by the army" in a Dutch passive sentence?

We use the preposition door. Whenever you want to mention who or what is actually performing the action in a passive sentence, you introduce them with door (which often translates to "through", but means "by" in this context).

Why doesn't the past participle veroverd start with ge-?