[Cicero]

Latin was the chief language of the western Roman empire. It remained the international language of diplomacy after the various vernaculars started to branch away: Italian, French, Spanish, and so forth. Greek was more or less lost to the West, except for a few scholars here and there.

Even English is full of words with Latin roots, which makes it an easier language to learn than Greek.

[maryz]

It remained the international language of diplomacy after the various vernaculars started to branch away

And of scholarship into -- I think -- the 18th century anyway.