Two independent clauses without a conjunction?

[musicgold]

Hi,

What is the role of the bold phrase in the following sentence? Is it acting as an adjective phrase or as an adverb phrase? I am not clear as to how these two seemingly independent clauses are connected together without any conjunction.

It was the first time that insurgents had partly breached any of the three dozen jointly operated outposts.

Thanks,

MG.

[Tdol]

Couldn't a case be argued for that?

3a. Used to introduce an anticipated subordinate clause following the expletive it occurring as subject of the verb: It is true that dental work is expensive. b. Used to introduce a subordinate clause modifying an adverb or adverbial expression: will go anywhere that they are welcome. (American Heritage Dictionary that. The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.)