Terrorism was abated because the government was doing a hundred other things to abate it like airline security and homeland security, things they are still doing.
I sure wouldn't have given my life to give Iraqis the vote to elect the Shiites in power in Iraq then kick the US out anyway, and I imagine the families of those fallen and crippled soldiers are now thinking the same to, asking themselves what the hell was the point?
We have all sorts of vulnerabilities that are not covered by our Homeland Insecurity Goombas.