sentence structure

Hi,

"The Anglo-Japanese alliance collapsed the day Britain refused to back Japan in its struggle against Russia, making it clear that Britain would henceforth defer to Russian power in the Far East."

"It is not an exaggeration to say that the Anglo-Japanese alliance collapsed the day Britain refused to back Japan in its struggle against Russia, making it clear that Britain would henceforth defer to Russian power in the Far East."

I know the first example works, but I am not sure if it would still work if I precede it with a preamble such as "It is not an exaggeration to say that," as in the second example. It just doesn't sound very natural to my ears.

What do you call this kind of sentence structure, whereby one sentence set offs another one that begins with a verb in progressive form?

Thank you so much.