The Treaty of Zaragoza was the one signed in 1529, but I think the Treaty of Tordesillas is much more well-known (mostly because the Treaty of Zaragoza basically restated Tordesillas and added another line on the opposite side of the world). I agree that the treaty that really divided the world was Tordesillas.
Yes, very obscure.
(It's where the Disgrace of Córdoba happened, when Germany lost to Austria in the 1978 world cup. We don't talk about it in polite company.)