Indirect rule is a type of government in which existing political elites and institutions continue to rule in a country.
The sentence, 'Indirect rule sowed the seeds for class and ethic tension' means that, indirect rule was the root cause, the principal reason why class and ethnic tensions occurred. The indirect rule was the factor that brings about class and ethnic tension.
It was that "Flat land with poor drainage led to salinization from irrigation waters," that was a factor in the decline of Sumer, since this led to a build up of salt in the soil, which greatly reduced agricultural output.
guptas made advances in the sciences. gupta philosophers proposed that the earth was not flat, but was instead round and rotated on an axis