Hitler attacked the USSR because he expected them to attack him at some point anyway and hoped to convince the Brits to accept the status quo on the continent (he even called on the allies to join in the war against the USSR in the declaration of war speech iirc).
The USSR kinda expected an invasion as well from Germany, just not so soon. So yes, Hitler did do pre-emptive assaults.
Hussein constantly denied having nukes, so no, he did not claim they had weapons of mass destruction, in fact, quite the opposite. He just frustrated searches for them, making people believe they were there anyway. Why else frustrate? Could in retrospect simply have been ego, base reluctance to be inspected (pride and arrogance) and irritation.
Regarding Iraq, to say "some people died" is a bit of an understatement. After putting Iraq on the verge of civil war and with currently estimates between 106.000 and 116.000 civilian deaths due to destabilising the region and population power balance over night.
http://www.iraqbodycount.org/
Most of these come from inter-sektarian and warlord militia violence. This type of violence was NOT present under Saddam Hussein (he did all the killing and political imprisonment himself). I'm not argueing the amount of freedom was greater or the current situation is worse, I can't really tell, tbh. From the looks of it, it improved in a lot of areas, but worsened in security.
So I'm stating the post-war policy of the Bush administration (especially the uncontrolled disbanding of the Iraqi national guard) is responsible for this. Which, is a direct consequence not of waging war, but of having no plan or idea for what came next. Particularly the incredibly stupidity of disbanding the Iraqi National Guard and with it basically creating both a large, combat trained disgruntled populace with no income and arming any group with a destabilising agenda that could abuse the power vaccuum (criminals, zealots, warlords, you name it).
And that is simply down to governmental shortsightedness, incompetence, lack of understanding of (and interest in?) the local situation and perhaps down to mere arrogance of "we'll fix it over night, they'll be transformed in democratic value loving people over night after they have been freed from tyrranny".
Plus, it would have been a much better reason and timing to remove Saddam Hussein during the Kuweit war. Nobody would have objected to the legitimacy of that. But no, US elections showed the hypocrisy of American foreign policy. The hypocrisy of supporting and condoning certain oppressive regimes as long as they are friendly towards the US or "stabilising" for the region. America often loses face through that hypocrisy. A lot of people believe America's only interested in preserving its own interests (and in doing so are not better than the USSR or China) and morality comes second to economic interest and political (world) power. Basically, when it's convenient, the democracy and "public outrage" card is pulled, but when it's not the US government looks away from uninteresting nations.
Basically, where would the US intervene? Rwanda or Middle East? Random poor populace genocide or dictator in control of oil threatening to not sell to the US in a time where oil resources becomes scarce and a certain country is the biggest consumer (and waster) of energy in the world?
What also annoys in general is that the US often does not conform to or participates in global treaties, despite being one of the main culprits to have the treaty signed. For instance, treaties regarding pollution and energy consumption, international law and other positive for the long term, worldwide initiatives. That creates resentment as well as strengthens the impression that the US is only interested in "#1" (economical self-interest with no regard for consequences).
And of course, the US often stampedes through porcelain cabinets despite of all that.