I don't think they have made a serious attempt to invade Konoha, ONLY raiding parties etc.
Do you think that Konoha could have stopped Killerbee and his team of Jounin's and 15 other Cloud Jounins:-
a) With Yondaime around...(easy answer)
b) Post Yonndaime, but with Sandaime at the age he was when he died
c) After Yondaime died, but with Jiraiya
d) Without Yondaime, Sandaime, or Jiraiya.
How would Konoha stop a Bijuu Blast from Killerbee?
The Point is that a Village's strength Varies up or down over time, AND it seems that the Cloud have always had some Over powered S-Class Ninjas plus more than a few Above average ninjas, and of course a lot of Fodder nin. My guess is that The Team that took down Nidaime of course Had two Kyuubi Power (Over-powered) ninjas, and probably Ten or more Above average to very strong Jonins with them.