The way I heard it, Pokemon was not very successful at first. Then they made the anime
series, and it started to catch on, game and anime started to fuel each other's popularity, and then there came the trading cards
and the merchandise
and it became the marketing juggernaut
we know now, which resulted in other people copying the concept (which, as even Pokemon haters will have to admit, is brilliant) and creating Digimon
I also heard that the Pokemon craze came at exactly the right time for Nintendo: the company was in financial difficulties after the Nintendo 64 disaster and might have gone under had not Pokemon revitalized the Game Boy platform and generally become a license to print money.
The accent in Pokeémon is incorrect, strictly speaking. The Hepburn romanization of the original title ポケモン (which is, of course, in katakana) is Pokemon. The accent was just added to prevent Merkin from mispronouncing it as "Pohk-mon".