How is a Theravada Buddhist monastery established? There is no Theravada monastery in the country I live in. I just read a short brief about lay people going together and forming a forest monastery in Norway, and was wondering about how a monastery is established?

Who initiates the process and who makes the decision (lay people, monastics, both in combination, or either)? Thinking in terms of whether it's just monastics moving back to their home country to spread the Dhamma, or if lay people gather support and invite monks. 

Not so much about the religious or practical considerations, just looking for a helicopter view.
Initially, it is the invitation of the laity to the Sangha, who then satisfy themselves that the support is adequate for their needs.  A lay community invites a Bhikkhu that they find particularly inspiring.  He finds a quorum of Bhikkhus to accompany him so as to maintain the Vinaya discipline. Lay communities often set up some kind of a committee so as to oversee and organise a physical accommodation, suitable for practice and religious observations: this varies considerably from one monastery to another.