Border Worlds

I have a question for anyone familiar with the recent history of the
Spinward Marches and it's environs:

What are the Border Worlds?

The Megatraveller Imperial Encyclopedia doesn't say anything about them
(that I have found), and I lost track of the goings-on in the Traveller
universe after the Fifth Frontier War.  Who controls the Border Worlds?
Are they a captive government?  Where do their sympathies lie?

Brian.
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