The invasion of Konohagakure was former Konoha ninja Orochimarus attemt to get revenge on his former village and teacher, the third Hokage, because he diden't became Fourth Hokage. While his own Otogakure was to small to take on Konoha, he found an ally in Sunagakure, who wanted to destroy Konoha due the fact that the Wind Daimyo had cut Suna's budget and started to send missions to Konoha instead of Suna.