Learn French: Pendant la guerre, il fallait survivre. - During the war, one had to survive.

Il fallait is the imparfait (past continuous) form of the expression il faut (it is necessary / one must). We use the imparfait here because 'having to survive' was a general condition or ongoing state during the entire war, rather than a single completed action.

Why does the translation say 'one had to' when the French uses il?

The word il in il fallait doesn't mean 'he'. It is an impersonal pronoun, just like the 'it' in the English phrase 'it is raining'. The literal meaning is 'it was necessary to survive', which we naturally translate as 'one had to survive' or 'we had to survive'.

Why isn't the verb survivre conjugated?

After the impersonal expression il fallait (just like with the present tense il faut), the action that needs to be done stays in its infinitive (dictionary) form. It literally translates to 'It was necessary to survive'.

Could I use pour instead of pendant to say 'during the war'?

No, to say 'during' a specific event or time period, you must always use pendant. English speakers often mix this up because 'pour' means 'for', but pour is mostly used for a purpose or a planned future duration, not for something that happens 'during' an event.