Realism, liberal institutionalism, constructivism | Political Science homework help

1- What is a structural theory? Choose one structural theory we have learned in class and using this theory, explain the so-called Coronavirus Vaccine-wars we currently observe.
2- Out of these three theories (realism, liberal institutionalism, constructivism), which one, do you think, best explains the European integration? Why? 

Guys this work needs a lecture background. So that, I am sharing the lectures also below. You may use relevant parts of the lecture as well as resources on the internet. Use examples from internet that supports the idea and give reference. However, be careful on plagiarism. There is a strict policy plagiarism policy.