The US has been materially helping ISIS capture the strategic eastern Syrian town of Deir El-Zour because it is a vital link binding together the territories of the Middle East’s Axis of Resistance.
The US is not fighting ISIS in Syria. Together with its ally Saudi Arabia it is using ISIS and other Wahhabi terrorist groups like Jabhat Al-Nusra to wage a war of aggression against Syria so that it can take control of Syria and gain possession of the resources of the Middle East.
Syria was targeted for destruction because of its key role in the Arab world’s Axis of Resistance against Israeli and US expansion. That is why Hezbollah – the other part of the Axis – fights alongside the Syrian army in the Syrian conflict, whilst Syria supports Hezbollah’s struggle in Lebanon.