I was in Mexico part of last week and over the weekend for my company's annual meeting. While there, I had the opportunity to visit the ruins of the Maya city in Tulum. It was exactly what I expected a Mayan city to look like, a city carved out of the jungle. The temple was impressive, right at the edge of a cliff leading down to the Caribbean. The Mayans didn't have a lot of tools and relied on human labor (and lots of it) to do the work. One possible reason for the Mayan decline is a revolt by the working class.
So how do we keep our working class from revolting? How can we keep the project team happy? Clearly, we don't want to work them to death. One company I've done some work with lately doesn't have a very sophisticated portfolio management project. Anyone can start up a project and expect the resources will be able to support it. The end result is that key resources are assigned to more projects than they can reasonably work in an 8 hour day. The solution here is a portfolio management process that looks at resource allocation and doesn't allow a project to go forward if resources aren't available to support it.
As for the Mayans, they declined but never completely disappeared. Even today a number of the Mayan languages are still spoken and other traditions still exist. I wonder if the same will be said about us in 1500 years.