Is "conservativism" a word?
Solution 1:
Merriam-Webster does not list conservativism, but Wiktionary does:
conservativism
- Alternative form of conservatism.
Conservativism is surely not a typo (as, say, consrvetism would be). It is legitimately formed from the adjective conservative and the suffix -ism. However, as you say yourself, conservatism is the much more commonly used term. The British National Corpus has 474 cites for conservatism, but only 3 for conservativism.
That being said, there are languages (e.g. German) in which the equivalent of conservativism (Konservativismus) is pretty much as common as the equivalent of conservatism (Konservatismus).