Imperial means pertaining to an empire or emperor.
Imperative means peremptory or urgent.
Imperious means authoritative.
1.Nothing can equal the imperial glory of ancient Rome.
2.The imperial crown of the emperor.
1.It is imperative that you should do it.
2.It is imperative that we take immediate action to reduce pollution.
1.He is very imperious and does not want to be contradicted.
2.An imperious manner.