In this sentence: "In the past, the small nation [ had been committed ] to self-managed socialism." Why is the past perfect used? Why not the past tense or present perfect?
If it was the only sentence, Past Simple would be fine. The use of Past Perfect indicates (in my opinion) that more events will be described later. Since they happened after the event described here it is OK to use the Past Perfect for the earliest event, and other past tenses (or present perfect) for later ones.