A lot of US allies have been responsible for funding Isis. The official story is that it is wealthy individuals within these allies e.g. within Kuwait, Qatar and Saudi Araba with countries like Turkey turning a blind eye whilst Isis were supplied through the Turkish border etc.
"America's Allies Are Funding ISIS
The Islamic State of Iraq and Syria (ISIS), now threatening Baghdad, was funded for years by wealthy donors in Kuwait, Qatar, and Saudi Arabia, three U.S. allies that have dual agendas in the war on terror.
The extremist group that is threatening the existence of the Iraqi state was built and grown for years with the help of elite donors from American supposed allies in the Persian Gulf region. There, the threat of Iran, Assad, and the Sunni-Shiite sectarian war trumps the U.S. goal of stability and moderation in the region.
It’s an ironic twist, especially for donors in Kuwait (who, to be fair, back a wide variety of militias). ISIS has aligned itself with remnants of the Baathist regime once led by Saddam Hussein. Back in 1990, the U.S. attacked Iraq in order to liberate Kuwait from Hussein’s clutches. Now Kuwait is helping the rise of his successors."
www.thedailybeast.com/articles/2014/06/14/america-s-allies-are-funding-isis.html
Read the whole thread. Isis was created to foment a Sunni/Shia clash, to try and topple Assad and to weaken Shia Iraq and has been equipped and supplied in order to do so. Syria has been fighting 100,000 terrorists from 7 different countries for a period of 3 years as the Syrian government supporter said on Radio 4.
It is part of a movement to foment a Sunni/Shia clash, to weaken the Shia Crescent, to redraw boundaries that were originally created by the Sykes-Picot agreement as well as the usual oil pipeline style battle to weaken governments trying to build a pipeline through Iran/Iraq/Syria rather than the Qatari backed pipeline.