It's all about territory.
Just like when you have one cat, it marks a territory around your garden & areas beyond. Then when a new cat comes to live in the area & dares to venture onto his territory. They will fight & the rest & eventually the cat gives up part of its territory to the new cat. As more & more cats come into the area a little more territory is given up & then their territories start to overlap as more cats take over. That is why late at night you can often hear cats crying like babies (whining).
“Woman was made from man; not out of his head to top him, nor out of his feet to be trampled underfoot; but out of his side to be equal to him, under his arm to be protected, and near his heart to be loved”