Question

The Ottoman Empire grew and expanded after it conquered the

Answer 1

Byzantine empire  i'm pretty sure                                                      

Answer 2

The Ottoman Empire, also known as the Ottoman Turkish Empire.

The Ottoman Empire began as one of the small Turkish states that emerged in Asia Minor during the decline of the Seljuk Empire.

The Ottoman Turks gradually controlled the other Turkish states, and continued to expand at the expense of the territories of the Byzantine Empire.

The answer is: Byzantine Empire.