A question about military manpower vs population

[Hunpecked]

No tax payers, no income. No income, no military budget. No military budget, no fleets of superdreadnoughts to go boom.

That was basically the theme of historian Paul Kennedy's book "The Rise and Fall of the Great Powers". In the beginning of the book he showed how 16th Century Spain, probably the wealthiest European nation at the time, eventually bankrupted itself through economic mismanagement and overly lavish military expenditures relative to its financial resources (i.e. taxpayers). In more recent times, the attempt to maintain an oversize military was a factor in the economic collapse and eventual dissolution of the Soviet Union.

With regard to Starhawk's story, the fact that the fictional Icarans can fight successfully with a relatively minuscule military is probably a major factor in their ability to sustain the war decade after decade.