Conquering large chunks of the Inner Sphere bootstraps to conquering the IS clans bootstraps to attacking Homeworld Clans; if you assume everything is coming up roses.
Or they really thought that returning a historic battleship to Tharkad as a gift would win over the Steiners, they controlled the FWL through "Thomas Marik", and they had a solid alliance with Sun-Tzu Liao; giving them the richest house, the most militarily productive house, and the most devious house of the Inner Sphere, and 2 of the 3 houses least likely to suffer from a counterattack, plus the one with a border with the least-liked (living) Clan in IS.
The Jihad kicked off way too early, too. What happens in 5-10 years with more warships floating out of slips in FWL, more trustworthy recruits for the Shadow Divisions, and a better "recruitment" process for unwilling converts?
The WoB thought they had the blessings of God - thus everything would break their way, no?