Baptists Were Once All United? (II)

This posting will be a short follow up to the posting "Baptists Were Once All United?" (here).

If the Baptists were all united in faith and practice at the start of the 19th century, believing as the "Primitive Baptists" do today, then how can we account for the three major divisions in the Baptist family in the first half or so of the 19th century? That time period gave us first the Campbellite division, then the Hardshell division, and then the Landmark division. The first two divisions show that the Baptist denomination, though holding to core beliefs that were common to all three, yet differed in regard to soteriology. 

If the Baptists were all united on that subject, why the Hardshell and Campbellite divisions? 

The Landmark controversy showed that the Baptists were not all agreed on ecclesiology. 

What think ye?