Why do you think the ottoman empire was called the gunpowder empire

The Ottoman empire was the first empire to use gunpowder weapons in their armed forces to a trained, coordinated and large scale way. The use of field artillery and large cannons to batter walls of fortresses such as Constantinople was new and terrifying. Infantry units were also armed and trained in the use of firearms on a large scale.

byzantine empire is the answer i think you are looking for.

hope this : )