Yep, that is exactly right.  You need a monument or other civ improvements to generate some DC resources.

Tip:  If you highlight a unit in the training window (whatever it's called) at the bottom it will list what resources are required to build it.  Applies to crystal, iron, DC, etc.

- Manii Names

Thank you for the reply guys

Not sure if only one will be enough or worth it. But I´ll try them out and if they don´t cut it we could make a suggestions to the dev team about balancing them...