Why is $-NH_2$ group of aniline acetylated before carrying out nitration?

(N/A) Direct nitration of aniline yields tarry oxidation products in addition to the nitro derivatives.
In the strongly acidic medium used for nitration,aniline is protonated to form the anilinium ion $(-NH_3^+)$,which is meta-directing.
This leads to the formation of a significant amount of meta-nitroaniline along with ortho and para derivatives.
By protecting the $-NH_2$ group through acetylation with acetic anhydride,the reactivity of the amino group is reduced.
This prevents the formation of the anilinium ion and allows for the controlled nitration,making the $p$-nitroacetanilide the major product,which can then be hydrolyzed to $p$-nitroaniline.