Learn Russian: Агент работал в другой стране много лет. - The agent worked in another country for many years.

To express how long an action lasts, Russian uses a quantity phrase or the bare accusative case without any preposition. English speakers often mistakenly try to use для or на. However, для means 'for the benefit of', and на implies the duration of a result, not the duration of the action itself.

Why is the word for 'years' лет here instead of a form of год?

The word год (year) has an irregular genitive plural form: лет (which historically meant 'summers'). You must use лет after quantities of five or more, including adverbs of quantity like много (many), мало (few), and сколько (how many).

Why is the verb работал in the imperfective aspect?

The imperfective aspect is required here because the sentence focuses on the continuous duration of an action in the past. Whenever you state exactly how long an action took place using phrases like много лет (for many years), you are emphasizing the ongoing process rather than a single completed result.

Why does the adjective другой end in -ой in this sentence?