Student or Learner
Some people hoped to become rich while others to become famous. During the13th century, the powerful Mongolians had built a great empire in Central Asia. Many merchants set off to engage in lucrative trading activities with them.
1. Why is 'had' used in the sentence when time (during the 13th century) is stated?
2. Why is 'had' used when there is no first action mentioned?
For example, in "After he had done his homework, he went out", 'had done' is the first action followed by 'went out'.
Could somebody please explain to me the reason/s for the usage in the first sentence?