Saudis an Qataris funded them until recently.

The vehicles were given to Sunnis who were supposed to use them for the benefit of Iraq as part of their gift by departing Americans. The Americans did not think they were worth the cost to bring them back

The Sunnis turned them over to ISIS or ran away from the battle leaving them behind. 

The traditional rule is that the enemy of your enemy is your friend. But somehow the Western powers have changed that to the friend of their enemy is their enemy. That won't solve problems like this, because you can't go making enemies if you don't have enough friends.

ISIS have captured several oil wells and refinery , they are able to sell oil in the Black Market to many neighboring countries at much lower prices than OPEC. They are able to pay fighters up to $20,000 per week, that's another reason young disenchanted men join ISIS.They have the buying power, to purchase vehicles, weapons and the next will be nuclear weapon.

well i know it was not me

so when u joining up

who selling it to them?

hum $20,000 a week can I wuk for only one month and tek the rest of the year off ?

them people gon have have yuh strap on a bomb before payday

Might not be a bad deal.