Let's recap the history. We were first attacked by al Qaeda in 1993 with the murder of a CIA agent in front of Langley followed by the first WTC attack. One might ask why? According to speeches made by bin Laden, he didn't like the fact that we, the United States, were in Saudi Arabia. And why were we there? We were there because of Iraq. We were enforcing the "no fly zone" as a result of the end of the first Gulf War. Saudia Arabia's government wanted us there....and so did the United Nations. And this was a war STARTED by Saddam Hussein who brutally invaded his neighbor. He not only continued to shoot at our planes, he continued to defy the UN Resolutions, thumbing his nose at the world. After signing onto the Resolutions to save his ass, he reneged on everything he promised to do.
Secondly, Saddam Hussein did nothing for his people while he took BILLIONS in KICKBACKS for selling oil in violation of the UN's "Oil-For-Food" program. And all those BILLIONS have yet to be accounted for. We know he was a state sponsor of terrorism....Hamas, and others. It's becoming clearer every day that terrorists groups are loosely connected if not tightly connected.
There are enough indirect connections between Saddam Hussein and terrorists....and even al Qaeda, that it wasn't worth the risk to do nothing. This became even more obvious after 9/11.
So yes, it is definitely part of the War On Terrorism. And the world is better off , and safer, without Saddam Hussein in power. Even most of the nations they weren't involved in Iraq have admitted to that fact.