there is no religion called mohammadism . The people who follow prophet mohammad's religion peace be upon him is called "Islam " . the word Islam means " submission to Allah *("the name of the god in Islam , the creator of everything ,who has all the power knows what happens on earth & the skies , knows what hides in the hearts , the god of the muslims, the infidels & everything , capable of everything )& the one who believes in this religion called "muslim " .
The term Mohammedan was based in the idea that Christians were followers of Christ, therefore, Muslims should be followers of Mohammed. The term Mohammedan was used through much of the Middle Ages until it was replaced in most European languages with a form of "Musliman" (Spanish musulmán, French musulman, English musselman, etc.). English made the jump in the mid-1800s to calling Muslims by the Arabic term "Muslim", which the other European languages have yet to do.
Mohammedanism, therefore, was the antiquated term used in the West instead of the correct term used today: Islam.