A report provided by the US Senate Committee on Banking, Housing and Urban Affairs contains lists of weapons provided by the United States to Iraq, many of which - including aircraft - would later be seized by ISIS and probably later deployed in Iraq and Syria. These included an horrendous US-manufactured arsenal of chemical and biological weapons: including anthrax, botulinium, and E.Coli as well as human and bacterial DNA. Grotesquely, the United States, which had provided these weapons, has later accused the Syrian Government of using chemical weapons, and Trump has used this as an excuse to invade Syria.
Book: Indefensible: Seven myths that sustain the global arms trade
The quotes below are taken from
Paul Holden, Ed.'s Indefensible: Seven Myths that Sustain the Global Arms Trade was first published in 2016 by Zed Books,UK, a well-written and well-resourced book that brings us up to date with the trade and also explores its many motives. I don't know if it was overtly stated anywhere in the book, but I formed the impression that excessive arms are collected, bought, and sold by national leaders as a power display and that their buying and selling is a kind of social interplay between globally hypertrophied alpha apes, currying favour or swaggering at each other from the top of their weapons piles and taunting smaller apes. In this anthropological light perhaps we can understand North Korea's leader, Kim Jong-un's resort to nuclear weapons as North America teases him with ostentatious displays of military strength while the world press taunts him as mad. Similarly Gaddafi's purchase of over $30b worth of weapons from world powers was perhaps an unsuccessful attempt to palliate the ferocity of the mad apes in the west.
I was particularly interested to read the history of who sold weapons to the Middle East and was not surprised to find out that it is the same powers that are intervening there to 'stop wars'.
US helped Iraq build factories for chemical weapons
"In the early 1990s, the US Senate Committee on Banking, Housing and Urban Affairs released a report confirming that The United States provided the Government of Iraq with ‘dual use’ licensed materials which assisted in the development of Iraqi chemical, biological and missile-system programs, including: chemical warfare agent precursors, chemical warfare agent production facility plans and technical drawings (provided as pesticide production facility plans); chemical warhead filling equipment; biological warfare related materials; missile fabrication equipment; and, missile-system guidance equipment." 
Chemical and biological weapons made by US sold to the Middle East
"The list of biological material the US provided [to Iraq and which were later stolen by ISIS] was shocking, including anthrax, botulinium, E.Coli as well as human and bacterial DNA. There is credible evidence that when the US invaded Iraq in 1991, US troops were exposed to the very agents that the US had supplied, over and above fighting against the weapons whose acquisition the US had helped to fund and arrange. In the aftermath of the fall of Saddam Hussein, the world was witness to another type of blowback: namely, when an ally is provided arms but fails to stop those arms being stolen by enemies."
"[...]a 2014 UN Security Council Report noted that in June 2014 alone ISIS seized sufficient Iraqi government stocks from the provinces of Anbar and Salah al-Din to arm and equip more than three Iraqi conventional army divisions. Reviewing the evidence, the same report provided a chilling summary of the range of weapons ISIS has at its disposal:
From social media and other reporting, it is clear that ISIL assets include light weapons, assault rifles, machine guns, heavy weapons, including possible man-portable air defense systems (MANPADS) (SA-7), field and anti-aircraft guns, missiles, rockets, rocket launchers, artillery, aircraft, tanks (including T-55s and T-72s) and vehicles, including high-mobility mobility multipurpose military vehicles." 
ISIS took many weapons, almost undoubtedly including chemical weapons, which it probably later deployed in Iraq and Syria, but the United States, which had provided these weapons, later accused the Syrian Government of using chemical weapons, and Trump used this as an excuse to attack Syria militarily.
 Source: Holden, Paul. Indefensible (Kindle Locations 978-982). Zed Books. Kindle Edition.
 US Senate Committee on Banking, Housing, and Urban Affairs, Second Staff Report on US Chemical and Biological Warfare-Related Dual-Use Exports to Iraq and the Possible Impact on the Health Consequences of the War, 1995. 9Ibid, Chapter 1. 10Ibid, Chapters 2 and 3.
 Source: Holden, Paul. Indefensible (Kindle Locations 987-992). Zed Books. Kindle Edition.
 The Islamic State and the Levant and the Al-Nusrah Front for the People of Levant: Report and Recommendations Submitted Pursuant to Resolution 2170 (2014), S/2014/815, paragraph 39.
 Source: Holden, Paul. Indefensible (Kindle Location 1009-1015). Zed Books. Kindle Edition.