Learn Russian: За полтора года он лишился авторитета. - In a year and a half, he lost his authority.

The verb лишиться (to lose, be deprived of) strictly requires its object to be in the Genitive case. This is an example of the Genitive of Deprivation. In Russian, verbs that express losing, avoiding, or lacking something often take a Genitive object instead of a standard Accusative direct object.

What is the difference between using лишился and the more common verb for "lost", потерял?

Потерять is the everyday verb for losing something (like your phone or keys) and takes a regular Accusative object. Лишиться literally translates to "to be deprived of" and has a more serious, consequential feel. It is frequently used for vital, abstract concepts like authority, rights, reason, or even physical things like body parts.

Why is за used here to mean "in", and could we use через instead?

За plus the Accusative case is used to express the duration of time it took for a result to be achieved or completed. If you used через полтора года, it would mean "a year and a half later" or "after a year and a half" (pointing to a specific point in time), rather than describing the timespan over which his authority faded.

If за requires the Accusative case in this time expression, why is the word года in the Genitive singular?