I would leave the following message to the millionth generation:

"Congratulations on not following the path of my people. Gone and far behind you, though we may be, you must remember that a species devided is a species that is doomed to extinction.

All empires fail, and ours was no acception. They fail for the same reasons, and will always fail. So never allow yourselves to regress to imperialism.

Should you find yourselves on the brink of destruction, and even if not, do as we have and survive compendiums of your knowledge.. that it is not lost to the next civilization as the majority of knowledge from our ancestry was lost to us.

It is by retaining the knowledge that we gain, and teaching of our errors to our succeeding generations that we will break the cycle of ascending, self destruction, and regression.

As our knowledge is passed to you, so must you pass it to the generations of your distant future, that what happens to us befalls no one else and our species lives until it's extinction cannot be avoided."