Hi tanvis1120,

You are quite correct, the past perfect verb tense is used to denote an event that occurred before another event, some time in the past. In fact, there are two major uses of the past perfect verb tense.

First, as noted, the past perfect expresses the idea that something occurred prior to another action in the past (sometimes with reference to a specified time). Examples:

Brent only understood the play because he had read the book. (unspecified time in the past)
Brent did not have any money because he had lost his wallet. (unspecified time in the past)
Brent had never been to an opera before last night. (specified time in the past)

Second, the past perfect is used to show that something started in the past and continued up until another action in the past. Examples:

Brent had had that stereo for twenty-five years prior to it breaking down.
By the time Brent finished his studies, he had been in Victoria for over five years.

However, if the past perfect action occurred at a specific time, the simple past can be used instead of the past perfect when "before" or "after" is used in the sentence. This is important for the sentence you asked about:

Before the subprime crisis weakened the housing market, America, with its state of the art infrastructure and with multiple job opportunities for expats, was one of the most popular destinations for foreign investment.

Keep an eye out for "before" and "after" keywords to know whether you should use the perfect past or simple past form.

Also, keep in mind the following differentiation between the past perfect and simple past tenses:

"Had/has/have been" is usually used for something that was done in the past and still applies (multiple events).
"Was/were" usually applies to something done in the past that no longer applies (single event).

America was one of the most popular destinations, but that no longer applies.

And, of course, context is really important. Examples:

Brent had been running to get fit.
Brent was running to get fit.

These two sentences subtly emphasize different things. The first sentence suggests that Brent first started running for the health benefits, but now he runs for some other reason. The second sentence suggests that at one point Brent ran to get healthy, but he has since stopped running.

Thank you Brent and David for the detailed explanations !