Learn Dutch: De politie start de onderhandeling. - The police start the negotiation.

In Dutch, politie is a singular collective noun. That is why it takes the singular verb form start. English speakers often mix this up because 'the police' is treated as plural in English.

Can I use begint instead of start in this sentence?

Yes, De politie begint de onderhandeling is perfectly fine. The verbs starten and beginnen are mostly interchangeable. Starten is often used for official procedures, projects, or engines, but both mean to start or to begin.

How would I use this in an object control clause, like 'The mayor orders the police to start the negotiation'?

You could say De burgemeester beveelt de politie om de onderhandeling te starten. In this sentence, de politie is the object of the main verb (beveelt) but acts as the logical subject doing the action in the om ... te infinitive clause, which is the core of how object control works.

How do we know whether onderhandeling is a de or het word?

It is built from the verb onderhandelen (to negotiate) plus the suffix -ing, which turns it into a noun. In Dutch, all nouns that end in this -ing suffix are automatically de words.