The two sides in the Battle of Kurukshetra from the Mahabharata are the Pandava Army and the Kaurava Army. The battle lasted for eighteen days.

These are the sides in the conflict:
The Pandava Army
The Pandava Brothers:
Prince Yudhistira, Eldest son of Pandu
Prince Bhima, Second son of Pandu
Prince Arjuna, Third son of Pandu
Twin Princes Nakula and Sahadeva, Youngest sons of Pandu

The Kingdom of Panchala

The Kingdom of Matsya

The Kingdom of Dwaraka

Others Demon Ghatotkacha, Son of Bhima through the demoness Hidimbaa
Prince Abhimanyu, Son of Arjuna through Princess Subhadra of Dwaraka

The Kaurava Army
The Kaurava Brothers: Prince Duryodhana, Eldest son of King Dhritrashtra
Prince Dushasana, Second son of King Dhritrashtra
Various other Princes, the Ninety-eight other sons of King Dhritrashtra

The Kingdom of Hastinapur

The Kingdom of Anga

The Kingdom of Madra

The Tribe of Trigartha

The Kingdom of Dwaraka

The Kingdom of Sindh

The Rules of War
Two Supreme Commanders met and set up the rules of war. They are as follows:

1. Fighting must begin no earlier than sunrise and end exactly at sunset.
2. Multiple warriors may not attack a single warrior.
3. Two warriors may "duel," or engage in prolonged personal combat, only if they carry the same weapons and they are on the same mount (no mount, a horse, an elephant, or a chariot).
4. No warrior may kill or injure a warrior who has surrendered.
5. One who surrenders becomes a prisoner of war and a slave.
6. No warrior may kill or injure an unarmed warrior.
7. No warrior may kill or injure an unconscious warrior.
8. No warrior may kill or injure a person or animal not taking part in the war.
9. No warrior may kill or injure a warrior whose back is turned away.
10. The rules specific to each weapon must be followed. For example, it is prohibited to strike below the waist in mace warfare.
11. Warriors may not engage in any "unfair" warfare whatsoever.