The word combines grandeur with an excessive propensity. Its formation followed German or French models.
German and French models are alternatives, not two consecutive borrowing stages.
Sources
- Merriam-Webster: megalomania
The English formation follows German or French models.
- Merriam-Webster: megalo-
The element covers large size and grandiosity.
- Merriam-Webster: -mania
The ending can express an excessive propensity.
- Online Etymology Dictionary: mania
Also built on *mania* "madness": kleptomania, egomania