Military History/Persian gulf war.
Why did Saddam go to war with Iran and then invade Kuwait?
He was crazy.
Seriously, Saddam ruled over a secular state. Meaning that while the people were Muslim, he and his ruling party the Baathists were not. They were of the the Sunni Muslim sect, while the majority of the people were Shiite, which is the same sect as the majority in Iran. So, when the secular Shah of Iran was overthrown by the Ayatollah Khomeini a theocracy was installed, ruling Iran according to his interpretation of the Muslim religion.
Syria and Iraq were both ruled by their own Baathist party Sunni minorities. Khomeini called for a revolution in Iraq and Saddam did not take kindly to that. Adding to the tensions were numerous border disputes which involved oil.
Saddam also had support in the West, being seen as a way to control Iran.
Saddam, wanting to advance his own prestige and power of Iraq launched an invasion, thinking he might be able to destabilize the recently installed revolutionary government.
The war see-sawed back and forth much in the manner of WWI with both sides unable to launch a decisive offensive and after 8 years the war ended along the same lines at which it had begun.
Having failed to do what he wanted to do in Iran, he turned his sights to Kuwait 12 years later.
Kuwait was an invention, much like all the other Arab countries, of the Colonial powers of France and Great Britain. Back in the days when oil was first being discovered. France and Britain wanted to assure supplies of oil for their navies. To do this they divided up the Middle East and North Africa into areas of control. To do this they drew up boundaries for counties that did not exist prior to WWI. After the war countries such as Saudi Arabia, Syria, Iraq, Iran, Kuwait, the United Arab Emirates, Qutar and others sprang into being. It also allowed France and Britain to divide and conqueror as they did in Africa.
You see if you draw a boundary around an area in which one tribe lives they will sooner or later unite, find nationalism and boot out the minority ruling colonists. But if you draw a boundary and call it, Gabon, or Congo, or South Africa, or Nigeria, or Iraq, or Syria, and within its borders include a small portion of many tribes, then they will have difficulty uniting, because they are always fighting amongst themselves.
We see that legacy in Africa, and in Syria and Iraq and many other places. The Kurds for instance, are a very large population of people, but because of boundaries drawn by the Great Powers, part of them live in Syria, Iran, Iraq, and Turkey. If the Khurds had their own country it would be larger than Turkey or Iraq., but without a national voice, they are oppressed and murdered by the ruling majority.
So, Saddam invaded Kuwait on pretenses that they were "cheating" and pumping oil from under the national border and stealing it from Iraqi territory. This may well have been true, but in oil field parlance, and common law, its called "right to capture", meaning if I drill a well on my side of the property line between your oil lease and mine, and drain oil from under your property without my well crossing the line, then shame on you for not drilling a well and pumping the oil under your land. That is why you see the old photos with drilling rigs next to each other like picket fences.
So Saddam, thinking that the Saudis could not do anything and that the US would not be willing to, invaded. He miscalculated.
Now, there is something we don't talk about in the US as it would make a lot of people angry. I'll call it the Roosevelt Doctrine, as in Franklin Delanor Roosevelt, not Teddy, his cousin. What FDR agreed to do was to secure Saudi Arabian oil from outside interference. He did this when major oil was discovered in Saudi Arabia. The Saudis were concerned about the covetous looks they were getting from France and Britain and were afraid they might make moves to seize the oil fields. Instead, King Faud spoke with FDR and in exchange for the US guaranteeing Saudi independence, the Saudis let seven US oil companies move in to develop the oil. These companies were called the Seven Sisters and were companies that no longer exist under the names they had back then. They have either changed, or merged or were absorbed by other companies. They formed a company called the Arabian-American oil company to run the interests of all seven. Today we know it as....ARAMCO, which is wholly owned by the Saudi government and is now their national oil company with no foreign involvement except foreign workers. They rely heavily on US workers.
So when Saddam invaded Kuwait, we stepped in because it was a direct violation or threat to the FDR Doctrine guaranteeing Saudi oil. Now, the US does not get but a fraction of its oil from Saudi, most imports come from Canada and Venezuela. But seizure of the Saudi fields by Iraq would have given Saddam too much control over the world oil markets and the global economy. The US could not have that. So we intervened and sent Saddam packing and ten years later went back and finished the job.