Learn Dutch: We zullen de politie waarschuwen als we gevaar zien. - We will warn the police if we see danger.

This is because of the word als (if). Als is a subordinating conjunction, which means it introduces a dependent clause and pushes the conjugated verb (zien) to the very end of that clause.

Why is waarschuwen placed right before als, instead of next to zullen?

In the first part of the sentence (We zullen de politie waarschuwen), zullen is the conjugated helper verb in the standard second position. In Dutch, helper verbs push the main action verb (the infinitive waarschuwen) to the end of its clause.

Can als mean "when" in this sentence instead of "if"?

Yes! In Dutch, als can mean both "if" and "when" for present and future events. Depending on the context, this sentence could absolutely mean "We will warn the police when we see danger."

Could you just use the present tense here instead of zullen?

Yes, you can. Dutch often uses the present tense to talk about the future, so We waarschuwen de politie als we gevaar zien is perfectly correct. Using zullen just makes it sound more like a firm promise or strong intention ("We will warn...").