To evaluate the ruling by military class starting from 1170 to 1270 in Goryeo dynasty, we need to define concepts of few terms. what is the coup de tat. It means revolt by military class. Interesting fact is that the term ‘coup’ does not imply the eventual consequences of revolt. it just describes event, tentative process to seize the power of court. It is necessary to distinguish successful coup and successful ruling afterward. After coup military officers can directly rule the country or they can be ousted by other military agent or they can peacefully pass the power to elected officer, other qualified agent. The second definition we need to think of is the term of regime. It is more complicated than defining the term ‘coup’. It is derived from politics in old greek polis to point out political structure to regulate people who belong to the regime. Regime consists of civilian body and institution.
Based on these two definition, I would like to raise few questions which are similar each other but imply different aspects of coups starting in 1170. the first question is why they did not change the kingship itself. of course they kill the 의종 and enthrone 명종 who are easier to control. they have practical power to make political decisions. however we can imagine further ambitions they can contain in their mind, to be a king. To be sure, it is more attractive option than becoming.
we also can recall some cases military classes get crown of country like napoleon in times of French Revolution. In stead they just chosen to rule the court under the sovereignty of king. was they just in lack of imagination or din’t they have a gut to sit on the chair of throne? It is not enough to explain whole situation.
To get better answer, we need to think about the concept of legitimacy. The definition of legitimacy in political field is to have authority. Authority consists of power to impose coercion to people and social consensus to be ruled. It stands for justified ruling. If so, topic moves to other questions like "how we can acquire legitimacy" and "eventually, who should rule." In general we can count few channels to acquire legitimacy. Lineage, election, power defined in armament are accepted as rightful way to acquire legitimacy.
However if we look back countries and societies, we can sense those three ways are not recognized equally. One way is priotized by another by social features and time. Some country value blood of lineage more than other ways. Other society and era put significant value on election. Goryeo dynasty, as its name reveals, valued consecrated blood to hold legitimacy. Goryeo was ruled under one family surname of 'wang'(王). Therefore the identity of society defined as Goryeo strongly contain the entity of wang family itself. the kingship as legitimacy holder by blood was powerful barrier from lots of ambitious threats. military government is also just one of threats in dynasty history. they are not ready to contrive way to solve the problem of legitimacy if they try to become the king. they were not willing to face those problems. It could be compared to another coup in Korea history which was actually succeed to change the regime. It was establishment of chosun dynasty. 이성계 as general of Goryeo dynasty rose revolt and change whole regime.
the second question but closely related with the first question is that legitimacy is for whom. When we go over reasons by military agents to justify their coups, we can find that they usually criticize about current governing system like Lax management, corruption, continuing unrest of society etc. those tendencies are found regardless of time. they criticize whole system is down. Then they say it is necessary to suspend whole system to back to the normal. However if we compare coups in premodern to coups in modern, we also realize there is difference in the people whom military classes should appeal to. In modern society, military class who commit a coup need to acquire the approval of civilian. Pledges are usually focused on development of county, better standard of living, more land and resources to exploit. Because people's consent is crucial point to justify coup. However In premodern times, subjects of country did not have enough political power and awareness to take influence on political issues. At that time military class focused on social hierarchy to get the approval of legitimacy. they tried to persuade civilian officer to are potentially willing to support them in managing government and to dissuade other military officers who can have potential power and willingness to subdue current military government from doing same action they did.
In cases of military government in Goryeo from 1170 to 1270, we also can find similar attitude to justify coup. First of all they tried to be tied with civilian officer's family by way of wedding. those actions mean two things. They wanted to assimilate legitimacy juries under the same family tree.