Similarly, when "lumps", concentrations of matter, begin to orbit a larger central lump, they interact gravitationally, disturbing each other's orbits, until they attain a pattern of relatively little disturbance. When they are orbiting in all directions, crossing each other's paths, they create more disturbance for each other than when they are all going in the same direction, and the same plain. Nothing more than this is necessary in explaining the evolution of the solar system or galaxy into a relatively flat plane of relatively circular, all-one-way orbits. Other factors, such as magnetism, no doubt also have influence, but are not as important.
Years ago, the Exploratorium in San Francisco had a computer that would show orbiting objects, and the effect of rocket impulses in different directions on the orbits. Is there a computer program which will show three or more objects in 3-D orbits (including the "sun", which "orbits" a joint center of gravity)? I've heard that the "three-body problem" is beyond the ability of computers to calculate. I think this came from the days of much less sophisticated computers.