how did napoleon ruin snowballs plans

Finally, Snowball completes his blueprint for the windmill. The animals hold a meeting at which Snowball wins over the majority with his descriptions of the leisurely life that the windmill will allow. Suddenly, Napoleon signals “nine enormous dogs wearing brass-studded collars,” which barge into the barn and chase Snowball out. Snowball manages to escape through a hedge.

Source(s): http://www.gradesaver.com/animal-farm/study-guide/section5/