BLASPHEMY!!!! NARUTO IS REEEEEEEEEEEEEALLLLLL!!!!!! xdBecause it's a story, not real life. Too many people on this site think about Naruto as if it's real life... And, as a story, jumping into a battle/war without an explanation would not make sense, and with Akatsuki starting slowly, and sending out weak people first, it lets the reader see some growth in Naruto and other characters. So, it was story, no other reason.
Seriously though, yeah, this is generally how most stories work.
Think about Dragonball Z, it's the ultimate stepping-stone manga/anime xd