Astrology actually is based on division.
You have four sets of signs,
yet still three sets of those signs are set in three sets.

Here is why it divides:

Astrology has three sets of characteristic signs:

The Cardinal
The Fixed
and The Mutable

Astrology has four sets of element signs:

Air
Water
Earth
and Fire

I am gonna list them below:

Air:Gemini,Libra and Aquarius
Water:Cancer,Scorpio,Ophiuchus and Capricorn
Earth:Taurus,Virgo and Capricorn
Fire:Aries,Leo and Sagittarius

Cardinal:Aries,Cancer,Libra and Capricorn
Fixed:Taurus,Leo,Scorpio and Aquarius
Mutable:Gemini,Virgo,Sagittarius,Ophiuchus and Pisces

Here is why they divide people up?
Each sign is of a different characteristic and element
and depending on if two elements can agree does determine a lot
and Astrology really is a tool used to conquer and divide.
Why it does not work is because they are not all humans,yet some animals.