The situation's more similar than you think. One of the reasons why the USSR ultimately failed was because their economy couldn't support a costly, prolonged war in...wait for it...Afghanistan. There are other reasons, of course, but that was a major contributing factor.
I didn't think USSR actually had a economy as everything including bread was manufactured by the government and sold at subsidized rates.
But prolonged war can bleed any country to death, specially if you don't what what and why you are fighting it.