Learn Italian: Hanno annullato il festival a causa del maltempo. - They canceled the festival because of the bad weather.

A causa di is the base phrase, but when it is followed by a noun that needs a definite article (like il maltempo), the di combines with that article. Here, di + il becomes the articulated preposition del.

Could I say per colpa del maltempo instead?

Yes, and it would be perfectly natural here! While a causa di means a neutral because of, per colpa di means due to the fault of and is used to assign blame. Since bad weather ruining a festival is a negative event, Italians often blame the weather by saying per colpa del maltempo.

Festival is a borrowed English word. How do we know to use the masculine article il?

In Italian, foreign loan words ending in a consonant are almost always treated as masculine by default. Another handy rule for foreign loan words is that their endings do not change in the plural, so the festivals would simply be i festival.

Is maltempo always written as one combined word?

Yes, it is a compound noun made from mal (bad) and tempo (weather). Italian often forms new single words by attaching mal directly to the front of another noun, such as malumore (bad mood).