The difference between absolute monarchy and centralization is that

History mainly revolves around the struggle between "central and local" and "monarchical power and relative power". It's unfolding.

Centralization refers to the relationship between the central and local governments. If the topic involves the central and local governments, it is generally answered from the perspective of centralization. For example, the county system, the parallel system of counties and countries, and the provincial system learned in textbooks all talk about how the central government can contain local governments step by step, narrow local power and expand central power. This is centralization.

Imperial power, that is, absolute monarchy, occurs in the central government, because the protagonist is the emperor, which refers to the concentration of individual rights of the emperor, that is, the relationship between monarchical power and relative power. If the topic involves how the emperor personally expanded his power step by step and reduced his relative power, it is absolute monarchy. For example, the six-department system in the three provinces of Sui and Tang Dynasties mentioned in the textbook was weakened step by step until Zhu Yuanzhang abolished the prime minister system and Yongzheng established the Ministry of War, until the power was abolished and the monarch's rights were strengthened.

I just finished the college entrance examination and summed it up myself.