alley_skywalker | DE War losses/victories ??

Here's what I never understood. How is it that the DEs were able to take control of the Ministry (and Aurors) in under 2 years during the Second War, effectively winning the war, with the exception of a very strong guerrilla resistance in the face of the Order/DA/Harry and co., but they were not able to do the same during the First War, which dragged on for about a decade, but at least five years if we assume that it didn't really get going until the mid-70s? It seems to me that the DEs would have been much stronger the first time around and would have had a lot more things going for them: a more stable-minded leader, more resources, more people willing to join (not having been exposed to the disaster of the a civil war yet), more time to prepare (both politically and otherwise). Sure, the Ministry was in denial for about a year after Voldemort's return and there was a lot of misinformation going around, but even then there is a gap of a year before the Ministry was taken and after it was clear that Voldemort was back and a war was inevitable. A year in which the Ministry/Aurors would have been actively working against DE threats and infiltrations. On the other hand, the DEs were likely to be markedly weaker and under-resourced the second time around.

So what changed? Why was the government take over so comparatively easy the second time around? Did they just not try for a coup the first time? But why in the world not? I don't remember canon giving a coherent explanation to this, but I won't discount that I'm forgetting things. (It's been a while.)

Any theories?