Saigo helped broker to supply Chōshū with the weapons

The following explains the part of modern history of Japan.

Also, Choshu desperately needed modern weapons, but had very limited contacts with the western powers. Satsuma, on the other hand, had developed a substantial arms trade with http://en.wikipedia.org/wiki/Great_Britain via http://en.wikipedia.org/wiki/Thomas_Blake_Glover, a http://en.wikipedia.org/wiki/Scottish_people merchant affiliated with http://en.wikipedia.org/wiki/Jardine_Matheson. At the suggestion of Sakamoto, Saigo helped broker an agreement to supply Choshu with the weapons it needed to fight the Tokugawa shogunate.^{http://en.wikipedia.org/wiki/Satch%C5%8D_Alliance#cite_note-2}

I'd like to know what role "an agreement" plays in the clause.
Thank you in advance for your help.