Sadly, our government has had some "beavis and butthead moments" when it comes to managing resources in war zones. Check out this vice documentary a couple of years ago of how much money was wasted by our government in Afghanistan.
Government Bureaucracy can be pretty inefficient, especially when you have a government that has free reign with resources as long as its supposedly used against some abstract threat of terror (especially true with the massive public support the bush administration had from the public and congress following 9/11 which led them to overstepped a lot).
However, that isn't the issue in this case. One, as I said, ISIS resources aren't only due to weapons supplied to rebel groups in Syria but also weapons held by the Iraqis who once again were not made up of disciplined soldiers and would run in fear from the enemies and leave behind all their crap. Its not a conspiracy and lie that ISIS now controls vast amounts of land in northern Iraq and southern Syria.
Also as I've said, the US has minimized weapon supplies to rebels once questions started to come out about who was getting our weapons in Syria.
Dude this thing is multifaceted and I can go all day highlight all the bits and pieces to the puzzle. I would recommend reading a bit more outside of the occasional news story. If your understanding of the situation is simply that American's supplied weapons and ISIS happened to get some of that from other groups, I would recommend you read some more. For example, learning about the sectarian conflict that existed in Iraq under Maliki which led to dissatisfaction amount sunni groups and former members of the Hussain era government and military and how many of those went on to join groups like ISIS.There is a lot of history there that paints a clear picture of the situation.
Highly overlooked point by outsiders.
1. U.S came took Iraq from Saddam ( a tyrant who was suppressing 80% shias for decades)
2. Gave the power to Paul bremmer ( huge mistake) - one of his policies days after he came to Iraq was de-baathfication, Civil servants, military etc basically everyone working for the govt. disbanded - What were they supposed to do???
3. Elections were after 1st battle of Fallujah ( U.S paid $400 mill to Sunnis to help them fight off insurgency and brought partial peace)
4. U.S puppet took office - Maliki, a Shia - all he did was consolidate Shia power and suppressed Sunnis ( killing, imprisoning, margnializing) even the Sunnis who were cool now turned to Al Qaeda in Iraq ( later ISIS)
5. ISIS took advantage of that plus the Syrian civil war and recruited thousands ( both local and foreign) , overran cities, amassed wealth, declared a Caliphate in July 2014.
now you got idiots who claim this group cannot shoot a full HD video with different angles and all kind of fukkery, i'm truly amazed. The ultimate goal of ISIS is to go war with the West in Dabiq ( a town in Northern Syria) - on some apocalyptic b.s about the end of times, They will do anything in their power to provoke western intervention and boots on the ground that includes beheading journalists and running mofos with tanks. I am truly amazed by people man.
and then we find out 30 years later when documents get declassified that all our "ally's" were funding both sides like always.
yea I'm a have to miss that one.
I'm trying not to relive it, breh