Breakdown of Мы хотим, чтобы посол подписал мирное соглашение.
мы
we
хотеть
to want
подписать
to sign
чтобы
in order to
Questions & Answers about Мы хотим, чтобы посол подписал мирное соглашение.
Why is подписал in the past tense if we want him to sign it in the future?
This is the core rule for чтобы when there are two different subjects (here, we and the ambassador). To say you want someone else to do something, Russian requires чтобы followed by the past tense of the verb. It expresses a desired action, not an action that already happened.
Why can't I just say Мы хотим посла подписать, like in English?
English uses an infinitive structure (want someone to do something), but Russian does not. When the person who wants the action is different from the person doing it, you must split the sentence into two parts connected by чтобы, giving the second part its own subject (посол) and a past-tense verb (подписал).
Why use the perfective verb подписал instead of the imperfective подписывал?
We want the ambassador to perform a single, completed action that produces a specific result: signing this specific peace agreement. If we wanted him to be in the habit of signing peace agreements regularly, we would use the imperfective подписывал.
Why doesn't the ending of мирное соглашение change? Isn't it the direct object?
It is the direct object, so it is in the accusative case. However, соглашение is a neuter noun, and inanimate neuter nouns look exactly the same in the accusative case as they do in the nominative (dictionary) case. The adjective мирное (peaceful) also matches this neuter accusative form.