The sentence suggests that They had helped each other for many years. Option D
The given passage implies a positive and cooperative history between the two countries. The references to "heartfelt letters" and the desire for "peace and goodwill" indicate a pre-existing relationship marked by mutual understanding and collaboration.
Terms like "peace," "good will," and "hope" also allude to a past relationship that was marked by cooperation and support for one another rather than hostility or conflict.