We're not there (now) because of Saddam, or WMDs, or even ISIS. We are there to:
1. Undermine the "Shia crescent". The US doesn't want the Iranians to have an unrestricted land corridor that extends from Tehran to Beirut. It is considered a security threat to Israel and Saudi Arabia. Saudi Arabia is the key to OPEC, and OPEC supports US Petrodollar dominance.
2. Restrict Chinese OBOR expansion. The lack of stability makes the region unviable for Chinese infrastructure building. This degrades China's ability to pivot away from their Sea Lines of Communication, which are currently a major economic weakness.
1. Undermine the "Shia crescent". The US doesn't want the Iranians to have an unrestricted land corridor that extends from Tehran to Beirut. It is considered a security threat to Israel and Saudi Arabia. Saudi Arabia is the key to OPEC, and OPEC supports US Petrodollar dominance.
2. Restrict Chinese OBOR expansion. The lack of stability makes the region unviable for Chinese infrastructure building. This degrades China's ability to pivot away from their Sea Lines of Communication, which are currently a major economic weakness.