Iran-Iraq War
The Iran-Iraq War was a war between Iran and Iraq that lasted from 1980-1988, which was closely followed by Iraq's annexation of Kuwait, and then the 1990 US Invasion of Iraq.
The Iran-Iraq war followed Iranian Revolution of 1979, in which Iran became a muslim country for the first time (prior to this, Iran had been a monarchy). This new independence led to fears amongst Iraqis about the backlash of the Iranian Shia majority, who, prior to the Iranian Revolution, had long been persecuted in Iran. There was a fear that they may begin to persecute Iraqi nationals in Iraq.
All of this fear was not real and was not based on any reality or any actual actions. Rather, the war began as a result of whispers and paranoia between Iran and Iraq, rumours whispered to them by foreign powers. The United States of America claimed that Russia was influencing the Iranians, claiming that they were aiming to control Iraq and steal their oil, while the Russians claimed that it was the United States that was influencing the Iraqis, leading them to believe that Iran were about to invade them.
Regardless of which nation was primarily responsible for the initiation of war, or indeed whether it was their own internal paranoia that began it, the war ended up being sponsored by Russia and the USA as one of the final plays as part of the cold war.
As the cold war became less important throughout the 1980s, Iraq's power rose above that of Iran's, as USA continued to support Iraq whilst Russia largely stopped supporting Iran, leading to Iraq's eventual victory. By the conclusion of the war, Iraq's forces were as much as 10 times as strong as Iran's, in terms of military technology and overall strength, thanks to the assistance of the United States. By this stage, Iraq had control of much of Iran's weaponry too, which led to a common lie during the 1990 invasion of Iraq that Iraq had been helped in their war by Russia - when it was actually Iran that Russia had aided.
The war ultimately achieved no major goal, with both nations impoverished at the end of it. To help to recoup the losses following this war, Iraq annexed Kuwait in 1990. This was followed by the US Invasion of Iraq and subsequent further impoverishment of the Iraqi people to extremes that are below their wealth even before they first discovered oil in the 1950s.