If i could add an addendum to this question. I have seen the spelling Moslems as well in older papers. Where does this spelling fit in?

As long as we're on the subject, does anyone mind if I ask about the term Mussulman? Wikipedia says it has become archaic, and I believe it appears in article 11 of the Treaty of Tripoli. When did this go out of fashion, and is it considered inaccurate the way Mohammedan is or is it just out of date?

I don't have an exact answer to your question, so this might be removed, but I can explain the term a bit more. Mohammedanism comes from a misunderstanding of Islam, conflating the way Muslims view Mohammed with the way Christians view Christ. In Christianity, Christ is viewed and worshiped as divine so his followers are 'Christian'. in the West, many people with a poor understanding of Islam assumed that Mohammed was viewed/worshiped in the same way as Christ by Muslims, thus they were 'Mohammedans', this term is very common in older texts and isn't some kind of prairie thing, the farther back in time you go the more common it is(especially when going back to the Crusades, for example, when people were concerned with portraying Muslims as heretics). This however, is incorrect, Muslims view Mohammed as a prophet, and the greatest of prophets, but very much NOT divine. The term has generally fallen out of use with a greater understanding of Islam itself and a realization that this was an incorrect assumption. I don't really have any specifics on when and how this came about, though.

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Sorry if this corny id a bit late.

Mohamedism (of variations of the name) was used from the very first interactions between the 'western' Christian world and 'eastern' Islamic world. The main reason Mohamedism was used in lieu of Islam stemmed from misunderstanding/lack of understanding of Islam by Christians. The understanding was that Islam must be like Christianity and the leading prophet was the most important figure. Christianity worships Christ, whence Christianity. It was (wrongly) believed that Islam worshipped Mohammed, whence Mohammedism. Unlike Christ in Christianity, in Islam Mohammed is not superhuman/god, Mohammed is a man who God (Allah) communicated the Quran to. Yes he also spread Islam and was the first leader of the religion and oversaw its initial growth, but beyond that he was only a man. As such, most branches of Islam offer Mohammed little reverence in a religious sense (going so far as to destroy tombs and sites where Mohammed was burried or lived etc). Only Allah should be worshipped. Labelling Islam as Mohammedism continued for centuries and as OP states can be found in textbooks up until rather recently. But as said, stems largely from a misunderstanding of the religion. There are several other reasons I have read that have contributed to the labelling, such as the fact lots of Muslims are called Mohammed. I am currently on my phone away from my books, but can post some sources later.