Invasions, the rise of eastern empire, Los of traditional tribes, economic troubles
Angle 1 is 77 because 37+66=107 and 180-107=77
The answer to the first question is 20% .
Ming, Chinese dynasty, had the hierarchical system in which rulers of all other countries were regarded as "younger brothers" of the Son of Heaven. Korea, as the closest neighbor was susceptible to tributes for this reason.