1. Downfall of feudalism
As more and more peasants died, the labor force shrunk. The surviving, healthy peasants were able to demand more money for their work. This money gave them new power and the social structures began to shift.
2. Downfall of Catholicism
Many people blamed God for the plague, as there was no other way they could explain it. They thought the Catholic church didn't do all they could've to help them, so they began to uncover the corruption within it.
3. Population decrease
Up until the plague broke out, the population had been steadily growing, especially with the introduction of new technologies and agriculture. However, the year the plague hit, you can see a sharp decrease in the world population, which continued to fall until the plague faded out.