Basically, over decades the US has armed Israel, and allowed it to develop nuclear weapons (the same ones no one else is allowed to have because er... only we're responsible enough or something) and used it to ensure that US policies in the middle east are adhered to. Whilst Israel is far from all powerful, it has significantly contributed to keeping the oil flowing where the US wants it to, and additonally also acts as control against perceived bad islamic states such as Iran. It's way way more complicated than that however, and would take a very long time to go through it all.