Twenty-nine years ago, Iraq invaded Iran.
The two countries would fight for nearly eight years, losing at least 300,000 and perhaps a million total killed in action combined at the high end of estimates (with Iran suffering 2/3 the total). The war was essentially a stalemate, although it may have blunted revolutionary Iran's immediate ambitions to dominate the Gulf. At best, Iraq won on points.
This First Gulf War, by bankrupting Iraq but creating a large military, set the stage for Saddam's invasion of Kuwait in 1990 and the subsequent 1991 Second Gulf War (aka, the Persian Gulf War or Desert Storm).
That 1991 war, of course, left Saddam bloodied but standing. It always seemed to me that there would be a reckoning eventually. The September 11, 2001 terror attacks provided the reason to take out Saddam in 2003 rather than risk his continued evil rule, support for terrorism, and pursuit of WMD.
As al Qaeda and Iran essentially invaded a freed Iraq, we fought from 2003 to 2009 another war inside Iraq to protect the new government and defeat al Qaeda terrorists, Baathist insurgents, domestic jihadis, and pro-Iranian Sadrist Shia death squads.
All that spun out from Saddam's invasion of Iran on September 22, 1980, which he believed would be a short and victorious war fought over the corpse of revolution-wracked Iran.