It is apparent that the three main warlords are representative of their chosen "commodity" - water, weapons, & gasoline. But, I believe they actually represent something greater - the cause of the apocalypse itself and each of them is in fact a representation of one of the four Horsemen of the Apocalypse.
Immortan Joe represents Conquest/Pestilence. We know that he pursues and enslaves people in the Wasteland (i.e. Furiosa's origin) and then turns those conquered people so they view him as god-like and the path to heaven. In this way, he assumes the same duality as the Christian horseman - as both a righteous figure (some interpret Conquest as Jesus spreading the gospel) and an evil figure (some interpret Conquest as a false prophet), and also as an infectious influence like the modern "Pestilence" (he "turns" his slaves into followers).
IJ and his followers also embody Pestilence by their own bodies. They are covered in festering sores, are mis-shapen and/or disabled, and have tumors from the nuclear radiation (side note: I find it interesting that Fury Road is the first time Miller has basically beaten everyone over the head with "It was global thermonuclear war, dummies!", when the series has only ever strongly hinted at that before).
The Bullet Farmer represents War. This is an easy one but hear me out. The Christian horseman isn't simply the embodiment of all war, it is the embodiment of unchecked aggression and "non-righteous" conflict. In a modern sense, War is simply unchecked militarism and internecine warfare. The Bullet Farmer doesn't merely represent these qualities, he actively pursues them. When the rest of the group is stuck in the mud and the three warlords have a talk, The People Eater tells him to wait and not hurt the "wives", but instead he goes riding off alone (unchecked aggression) and fires wildly with no regard to who he hits (collateral damage/internecine warfare/"friendly fire").
The People Eater represents Famine. "But he's fat!", you say. Read on, this requires more backstory of the Christian horseman. Famine is generally shown carrying weighing scales to measure grain during a famine. When he appears Saint John hears an exclamation on the prices of grain, but it then concludes:
and see thou hurt not the oil and the wine
Why does the voice say this? It's generally interpreted to mean that luxury goods should remain unaffected by famine, meaning the rich will not suffer, while the poor will. In this way, Famine also embodies the injustice and gluttony of the rich. We see this reflected in the characters surrounding The People Eater - many will resort to eating mutant salamanders, whereas TPE is extremely obese and has major gout, he is obviously well-fed.
TPE also embodies Famine in his name. Throughout history there are recurring episodes of cannibalism practiced by people who were not getting enough nutrients.
So, I bet you're wondering "who's the fourth Horsemen???"....it's Max. Max is Death. Nowhere is this more clear than Max's visions of the dead people he has been unable to "save". He carries the dead with him, leaves people dead in his own path, but can also never be killed himself. Max and Death are both remorseless forces of nature, and that is especially true in Fury Road.

A 50kg (7st 9lb) silver bar was brought to shore on Thursday on the island of Sainte Marie, from what is thought to be the wreck of the Adventure Galley.
The bar was presented to Madagascar's president at a special ceremony.
US explorer Barry Clifford says he believes there are many more such bars still in the wreck.
Capt Kidd was first appointed by the British authorities to tackle piracy but later became a ruthless criminal and was executed in 1701.