First time in Iraq, we followed Gen. Colin Powell's rules. "Powell Doctrine"
Second time we ignored Powell's rules. The size of the invasion force was too small. The enemy went into hiding, to wait us out.
It is worthwhile to understand the Powell Doctrine. It was the result of analysis of Korea and Vietnam, and getting bogged down with unending war--which is pretty much what we have done since 9-11-2001.
https://en.wikipedia.org/wiki/Powell_Doctrine1.Is a vital national security interest threatened?
2.Do we have a clear attainable objective?
3.Have the risks and costs been fully and frankly analyzed?
4.Have all other non-violent policy means been fully exhausted?
5.Is there a plausible exit strategy to avoid endless entanglement?
6.Have the consequences of our action been fully considered?
7.Is the action supported by the American people?
8.Do we have genuine broad international support?[2]