In recent years, China has taken over from the United States as the world's leading economic power.

taken 是动词 take 的过去分词形式，take 的基本意思是"拿、取"。 over 在这里是介词，表示"在...之上""超过"的意思。 taken over 是一个短语动词，意思是"接管、取代、超越"，指一方取代另一方成为主导地位。