Did Sultan Mehmed the Conqueror abolish slavery first, and what is the historical overview regarding that?

We have been informed of what some writers have mentioned—and Allah knows best if it is true—that Sultan Mehmed the Conqueror stipulated in his era, as a condition for peace with Europe, the drafting of an agreement prohibiting slavery, and that it was the first international agreement to that effect. We have been unable to verify this matter from a reliable source. It should be known that slavery occurred in Islam for specific considerations, and that Islam encouraged the liberation of slaves and urged good treatment towards them.