How were there 80,000 ninjas in the Shinobi World War in Naruto? I have been watching Naruto anime for a few months and just started to watch Shinobi World War arc. I was shocked to see 80,000 ninjas assembled. Where did they come from? If we take into account that 5 countries and samurais make 6 countries total, each country would contribute around 12,000 ninjas. But only around 100 ninjas were seen in Konoha in the previous episodes. How did this number come from? Were they living in other villages under the orders of their respective Kage?
Let's approximate the size of the Hidden Leaf based on the size of the Nine-tails in his attack:



As you can see, the village is quite large. I can estimate a population of over 100,000 easily. Since many of them are shinobi, I don't think it's exaggerated to think that there are at least 12,000 shinobi there (probably more).

So that's where all of them came from. Don't forget that we are focusing on only one (two) set of academy students as they progress, in reality there are new (and old) classes every year that graduate, get their own Jonin sensei, and take on missions etc. Those unimportant characters are often seen as what I like to call "shuriken throwers" (they only know how to throw shuriken, nothing else). You usually see them die when a strong opponent arrives.