I won't nitpick the astronomy bits, but I would like to add something historical to the discussion.
In "The Roman Empire and Its Germanic Peoples," Herwig Wolfram asks the question of why the Eastern Roman Empire outlasted the Western Roman Empire by so long. The answer he comes up with is that the Western Empire had much greater concentration of wealth in the hands of the senatorial class. This meant that it was hard to collect taxes to pay for things like an army, and at the time of the invasions of the Goths and Franks, the Eastern Empire was collecting three times in taxes what the Western Empire was collecting, and thus spending more on their army than the Western Empire was collecting in taxes.
Without sufficient tax revenues he military machine could not sustain itself, and when three senatorial households had a budgets that combined equalled the entire tax revenue of the Western Empire these super-wealthy were just too politically powerful to tax. Wolfram also suggests that this is what doomed Ostrogothic Italy when they fought the Byzantines.
In "The Roman Empire and Its Germanic Peoples," Herwig Wolfram asks the question of why the Eastern Roman Empire outlasted the Western Roman Empire by so long. The answer he comes up with is that the Western Empire had much greater concentration of wealth in the hands of the senatorial class. This meant that it was hard to collect taxes to pay for things like an army, and at the time of the invasions of the Goths and Franks, the Eastern Empire was collecting three times in taxes what the Western Empire was collecting, and thus spending more on their army than the Western Empire was collecting in taxes.
Without sufficient tax revenues he military machine could not sustain itself, and when three senatorial households had a budgets that combined equalled the entire tax revenue of the Western Empire these super-wealthy were just too politically powerful to tax. Wolfram also suggests that this is what doomed Ostrogothic Italy when they fought the Byzantines.