The future in the past is used when we want to fast forward from a moment in the past to say what will happen at a later time. It’s usually an explanation inside a narrative.

We use a wide variety of tenses to express the future in the past, and these reflect the various tenses we use for the future when speaking in the present.

Italian uses the composed conditional in equivalent meanings but English avoids this form, so there can be some mistakes that arise from interference.