Merge similar databases

Hi

I have a system running postgresql that I have installed on two different
servers. My challenge is that I need another server that I can install the
same system but to be in position to combine the three different but similar
structure postgresql databases to have one main database.

I have a project that I am working on that is running in three different
countries. Now, My plan is to have a server in each of these countries and
later have one main server that contains all the data from these three
countries.

Is this possible? if yes Main someone help me set this structure up.

Thank
Martin