*Iraq*
The Gulf War[b] was an armed campaign waged by a United States-led coalition of 35 countries against Iraq in response to the Iraqi invasion and annexation of Kuwait.
«The Iraqi military invaded the neighbouring State of Kuwait on 2 August 1990 and fully occupied the country within two days. Different speculations have been made regarding the true intents behind the invasion, including Iraq's inability to pay Kuwait the more than US$14 billion that it had borrowed to finance its military efforts during the Iran–Iraq War, and Kuwait's surge in petroleum production levels which kept revenues down for Iraq.[28] Throughout much of the 1980s, Kuwait's oil production was above its mandatory OPEC quota, which kept international oil prices down.[29] Iraq interpreted Kuwait's refusal to decrease its oil production as an act of aggression towards the Iraqi economy.[30] The invasion of Kuwait was met with international condemnation, and economic sanctions against Iraq were immediately imposed by the United Nations Security Council in response.»
So it was Saddam Hussein who invaded his neighboring country. Also note that the affected countries asked the UN to set things straight here. The US did, in concert with 34 other countries.
With Saddam still in power after that, there was an agreement that Iraq should destroy its stockpile of weapons of mass destruction. In the build up of the war, Iraq did not comply:
«The inspections were carried out by the United Nations Special Commission (UNSCOM). UNSCOM, in cooperation with the International Atomic Energy Agency, worked to ensure that Iraq destroyed its chemical, biological, and nuclear weapons and facilities.[85] In the decade following the Gulf War, the United Nations passed 16 Security Council resolutions calling for the complete elimination of Iraqi weapons of mass destruction. Member states communicated their frustration over the years that Iraq was impeding the work of the special commission and failing to take seriously its disarmament obligations. Iraqi officials harassed the inspectors and obstructed their work,[85] and in August 1998 the Iraqi government suspended cooperation with the inspectors completely, alleging that the inspectors were spying for the US.[86] The spying allegations were later substantiated.[87]»
Bush decided to get rid of him on the basis of false suspicions (weapons of mass destruction and involvement with 9/11):
«The United States based its rationale for the invasion on claims that Iraq had a weapons of mass destruction (WMD) program[68] and posed a threat to the United States and its allies.[69][70] Additionally, some US officials falsely accused Saddam of harbouring and supporting al-Qaeda.[71] In 2004, the 9/11 Commission concluded there was no evidence of any relationship between Saddam's regime and al-Qaeda.[72] No stockpiles of WMDs or active WMD program were ever found in Iraq.[73] Bush administration officials made numerous claims about a purported Saddam–al-Qaeda relationship and WMDs that were based on sketchy evidence rejected by intelligence officials.[73][74] The rationale for war faced heavy criticism both domestically and internationally.[75] Kofi Annan, then the Secretary-General of the United Nations, called the invasion illegal under international law, as it violated the UN Charter.[76] The 2016 Chilcot Report, a British inquiry into the United Kingdom's decision to go to war, concluded that not every peaceful alternative had been examined, that the UK and US had undermined the United Nations Security Council in the process of declaring war, that the process of identification for a legal basis of war was "far from satisfactory", and that, taken together, the war was unnecessary.[77][78][79] When interrogated by the FBI, Saddam Hussein confirmed that Iraq did not have weapons of mass destruction prior to the US invasion.[80]»
Like I said somewhere else, the war on terror was a horrible brain-dead response from Bush. It really has tainted the image of the US, and the misjudgement here has traumatized the US so much that the average Joe wants no foreign policy anymore and hide under his blanket.
However, the background of the war has nothing to do with the theories you will find on twitter. The US made the wrong call here, it was not a selfish move to make a profit from as you will find in "might makes right".
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*Afghanistan*
Bin Laden was leader of the Taliban, which was de facto the government of Afghanistan. By attacking the US on 9/11 the Taliban made an enormous risky move as they opened war with the US. Still, the response of the US was reasonable: extradite Bin Laden. Afghanistan did not comply.
You can rightly question whether the US response was smart here. But you cannot deny that the Taliban opened the conflict with the act of war on the US.
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*Syria*
Are you serious? It's dictator kills the people for asking democracy. Remember the Arab Spring? Young people in the middle east were fed up with severe (religious) oppression, no social mobility and the rule of dictators, they asked for democracy. Putin quickly came to the rescue of said dictators to make sure democracy would not win.
You rather should accuse the US for not taking responsibility, the red line of Obama turned out to be not so red. Here the US has shown to be too tired of war and too confused to fulfill its role.
I recommend to read the article here: https://en.wikipedia.org/wiki/Syrian_civil_war