Complex sentence: At first, the foundation was calling for a shrinking population in order to create a better living environment for the Dutch; later on the emphasis was put on a reduction of the ecological footprint of the inhabitants of The Netherlands.
Split into simpler sentences: At first, the foundation was calling for a shrinking population in order to create a better living environment for the Dutch. Later on, emphasis was put on a reduction of the ecological footprint of the inhabitants of The Netherlands.