Most governments, at one time in the eighties, passed declarations saying that government contracts for communications equipment must conform to international standards. I believe that the main reason for this was to break the stranglehold which IBM's SNA protocol held on large segments of the dataprocessing market; others might disagree.
Given the standards-political climate of the time, this meant ISO standards.
The problem with this was that at the time, products implementing ISO standards were few and far between. So, organizations chose one of two approaces:
Recently, more and more governments have taken to revising their documents, allowing or even requiring TCP/IP at the network layer, and allowing a choice between Internet protocols or OSI protocols at the service layer. The only two protocols that have seen some significant deployment as a result of the GOSIP mandates are X.400 and X.500.