Whilst there are numerous lessons worth learning from the first world war, one interesting take away for me was how the allies learned to use teamwork on the battlefront through a series of bloody lessons.
At the start of the war, whilst elements of the military fought side by side, they did so pretty much independently when on the battlefield (i.e. silo mentality).
By 1918 however, the concept of an Arms System was fully in place. This meant the heavy artillery, tanks and rifle carrying soldiers worked together to much greater effect, aided by primitive comms systems.
As an aside, the Americans didn't have the benefit of that experience and so when they deployed using old school techniques they still had tough lessons to learn.
TAKE OUT: once again, the benefits of collaborative working are there for us all to see... you just need to ensure the Purpose is motivating and powerful enough to rally everyone.