The Nation of Islam is more of a social movement. It started in the 30's by an African American man by the name of Fard Muhammad. The Nation claims Muhammad is an incarnation of Allah...The Muslim God.
The religion become more popular during the Civil Rights era in the states when leaders like Malcolm X and Louis Farrakhan became household names.
The religion is mostly comprised of African Americans who are strong advocates of black rights.
Now, traditional teachings of Islam say there is only one God and that God works through prophets rather than assumes a physical form, such as Fard Muhammad.
The belief in Islam is defined by the Five Pillars of Islam, which include daily prayer, faith, fasting, charity and a pilgrimage to Mecca.
Members of the Nation of Islam do not follow the Five Pillars of Islam. So that's why many Muslims consider them to be two completely separate religions.