The following is a brief background of the build up to the Syrian Civil War and a collection of sources showing how the US and it's allies have both directly and indirectly created the situation which has given rise to ISIS.

In the period following the Second World War, the US has engaged in covert operations and coup attempts in Syria due to their support for Socialism and Russia:

http://en.wikipedia.org/wiki/CIA_activities_in_Syria

This means that the primary choice of opposition was radical Sunni Islamists due to their rejection of the inherent secularism of socialist leaning governments:

http://www.globalresearch.ca/syria-s-uprising-in.../29221

This has lead to decades of violence and conflict between the Syrian government and the Sunni radicals, and terrorist attacks against Syrian Christian and Alawite minorities. The Sunnis due to their lack of political dominance in the country have instead resorted to terrorist attacks against civilians and government officials in order to oppose the secularism of the Syrian government, the government forced into a position to protect Syrian civilians has lead to increasing violence between the two factions.

http://en.wikipedia.org/wiki/Terrorism_in_Syria

Unfortunately, Syria's current uprising is not secular or based on the desire for democratic reform. The majority of the Syrian protesters and rebels have always been dominated by radical Sunnis who have wanted a government based on Sharia.

“Syria’s uprising is not a secular one. Most participants are devout Muslims inspired by Islam. By virtue of Syria’s demography most of the opposition is Sunni Muslim and often come from conservative areas.”

http://foreignpolicy.com/.../islamism-and-the-syrian.../

Iraqi politicians stated numerous times that if the US backed the Syrian rebels it would destabilize Iraq, which as they called, happen exactly as they said it would.

“The idea that secularists and moderates ever had a chance to be the dominate rebel military opposition in Syria is a nonsensical fantasy.” -Patrick Cockburn

https://www.youtube.com/watch?v=Z2E8XBnQVfE

Time and again it has been shown that the largest benefactors of US support for militia and rebel factions in Syria, whether by direct or indirect means, is going predominantly toward radical Islamists. The US has been warned by countless world leaders, journalists, analysts and experts that our policies are benefiting and creating the very same terrorists we have sworn to destroy.

“We Helped Build ISIS” –Admits retired Lt. Gen. Tom McInerney

ISIL created by US, says CIA contractor

Iraq Crisis: ISIS Terrorists were Trained by US in 2012 for Syria Conflict

Al Qaeda Commander claims US helped create and supports ISIS

How the US Allowed ISIS to Form a Terrorist Army

US-Backed 'Moderate' Free Syrian Army Factions Join ISIS Terror Group

America's Allies Are Funding ISIS

US/EU ally Turkey Supporting ISIS:

http://www.al-monitor.com/pulse/originals/2015/01/turkey-syria-intelligence-service-shipping-weapons.html#

http://www.hurriyetdailynews.com/3000-in-turkey-linked-to-isil-group-police-intel-report-says.aspx?pageID=238&nID=77063&NewsCatID=341

US trained Syrian and Libyan Wahhabi terrorists:

http://www.washingtonpost.com/posteverything/wp/2014/08/18/the-terrorists-fighting-us-now-we-just-finished-training-them/

Iraqi politicians stated numerous times that if the US backed the Syrian rebels it would destabilize Iraq, which as they called, happen exactly as they said it would.

The idea that secularists and moderates ever had a chance to be the dominate rebel military opposition in Syria is a nonsensical fantasy.

-Patrick Cockburn

'Moderate' Syrian rebels sell Steven Sotloff to ISIS

ISIS commander who was killed was former US/NATO backed Libyan rebel leader

US-Backed 'Moderate' Free Syrian Army Factions Join ISIS Terror Group

1,000-Strong Syrian Rebel Brigade Defects to ISIS

FSA brigade 'joins al-Qaeda group' in Syria

The US is not supporting secular/moderate rebels according to the testimony of the FSA's southern commander:

"The bits of the FSA that continue to oppose Nusra and the Islamic State blame the West for their loss of power. ‘The Syrian people will welcome any support if the West continues to abandon us,’ the FSA’s commander for southern Syria, Abu Fadi, told me in Jordan. Abu Fadi said that, contrary to reports in the US newspapers, he had received almost no American help. None of his men had been trained in the camps that supposedly exist in Jordan. No weapons had been handed over. ‘We have had some new boots and jackets,’ he said with a snort. ‘That’s all.’"

The US had supposedly been training 'moderate' rebels in Jordan, why is it that the main opposition leader in the FSA is claiming otherwise? And let's not ask the Northern commander of the FSA because we already know he wants a government based on Islamic Law

Additionally, a western diplomat makes the startling revelation that the vast majority of Syrian rebels are Islamist thugs:

"The official was his government’s main conduit to the Syrian rebels. I asked him what percentage of the rebels western countries could support: what percentage were not jihadis, not committing human rights abuses, looting or kidnapping — and were militarily effective?"

"There was a silence. Finally, he said: ‘Thirty per cent.’ It was a devastating admission. Then he paused and said he had been considering only the first three criteria. Adding in military effectiveness, you would have to say the West could support only 10 per cent."

Hassan Aboud of Soquor al-Sham and Abu Ayman of Ahrar al-Sham, another Islamist group, said that whoever was vetting which groups receive the weapons was doing an inadequate job.

“There are fake Free Syrian Army brigades claiming to be revolutionaries, and when they get the weapons they sell them in trade,” Mr. Aboud said

FSA selling US TOW missiles to Syrian Jihadists

Here's the CIA supporting and supplying Islamists with arms in Syria (2012):

http://www.nytimes.com/2012/10/15/world/middleeast/jihadists-receiving-most-arms-sent-to-syrian-rebels.html

http://www.nytimes.com/2013/03/25/world/middleeast/arms-airlift-to-syrian-rebels-expands-with-cia-aid.html?pagewanted=all&_r=0

http://www.canberratimes.com.au/opinion/alqaeda-now-a-us-ally-in-syria-20120910-25oby.html

March 3, 2015- US backed Syrian rebels armed with anti-tank weapons defect to ISIS:

https://www.youtube.com/watch?feature=player_detailpage&v=HEqDRoQ2k9A&list=PL50BDB9BCCFAF09CA#t=30