Actually, the Cabal are not a militarized group of soldiers. Sit down, children. It has been said that the Traveler brings good fortune to all races it crosses path with. One of these races was the Cabal, millions of years ago. The Cabal were weak. Depressed. Unfed. The Traveler appeared, saw them, and gave them all food in the form of McDonalds, which gave them their obese shape. They loved the Traveler for this, but it was time for it to move on. It left. The Cabal were enraged, but did not know what to do about it. After the Halo rings were destroyed by John 117's daring escape onto the USS Interprise, a piece of the destroyed ring, called the Seeing Piece, flew through galaxies until landing on the Cabal's homeworld. This seeing piece told them where the Traveler was. Earth. They became mad, made a fearsome army, and set up camp on Mars, in an attempt to destroy humanity. Ovaries.