A pre-emptive strike is when you attack an enemy because you know he is about to attack you. Historically, most attacks launched under the "pre-emptive" strike doctrine have turned out to be questionable at best. The only really "legitimate" pre-emptive strike in history was arguably the Six-Day War in 1967. While it turns out the Arab states weren't about to attack Israel, their public sabre-rattling was beyond ridiculous and any reasonable person could have concluded they might be about to attack. The anti-Israeli rhetoric of middle eastern governments grew considerably more muted after 1967.
The attack on Iraq was never claimed to be a pre-emptive attack, as the idea that Iraq had forces poised to attack the USA didn't pass the laugh test. It was based on the even more diluted concept that this was a "preventative strike," the claim being that while Iraq was not able to attack the USA, they were secretly trying to acquire the means to do so.
So no, wasn't a pre-emptive attack.
As to why we are staying in Iraq after Saddam was gone and the claimed casus belli was eliminated, who knows. The west has been meddling in the Middle East since the end of the Ottoman Empire in WW1, and it's hard to see how it's benefited anyone except the oil companies.
Terrorism is a tactic, not an ideology. The whole "war on terror" thing is just a propaganda device to justify American militarism and foreign adventurism abroad. The fact that it is continuing under Obama, shows how little "change" we can expect.
The only people who can take away our freedoms are in Washington.