There are a lot of differences between the Iraq and Vietnam Conflicts.
In Vietnam the country was torn by war for nearly 20 years before we committed our first combat troops.
In Vietnam the Viet Cong were fighting to reunify their country.
In Iraq the Iraq insurgents(mainly Sunni's) are fighting to regain their brutal rule over the other 80% of the Iraqi population.
Vietnam had 2 superpowers(China and the Soviet Union) pumping weapons into North Vietnam, Iraq doesn't...they might get some weapons from Iran but other than that, the Insurgents are fighting with what they could capture before we reached the weapons dumps.
Vietnam had a Ho Chi Minh trail, Iraq doesn't.
We were fighting in a Jungle in Vietnam, we're fighting in mainly desert in a Iraq.
In Vietnam America bombed several South Vietnamese cities to rubble just trying to get the Viet Cong out, has you seen this happen in Iraq? SOME buildings are being destroyed but this is war, what can you expect?
Vietnam was supported by a well trained and equipped North Vietnamese army that was very popular in North Vietnam. Iraq insurgents are supported by no army, and are very unpopular throughout Iraq.
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Both sides about Iraq make good arguments, I'm not going to deny that, but Iraq is very far from being another Vietnam. If you really research the two wars, they're completely different. The only similarity being the Guerrilla tactics.
About the WMD's:
Iraq DID have WMD's, we've found roughly 500 weapons loaded with Sarin and Mustard gas in Iraq. Most of the chemicals are partially degraded and were most likely build pre-Gulf War, but Saddam said that he destroyed all of his weapons, and this was clearly a lie.
If Saddam couldn't keep track of all of the chemical weapons his country had, then how hard would it have been for a terrorist organization to march right into Iraq and take some of them?
One bomb loaded with Sarin even exploded in a road side bomb in 2004, 2 soldiers were treated for exposure, but the chemicals weren't mixed properly so the bomb didn't work in the way that the Insurgents had hoped.
But if they were mixed properly, that amount of Sarin would have been enough to kill more people than everyone who died in 9/11.
http://www.mensnewsdaily.com/archive/m-n/mariani/2004/mariani052804.htm
http://www.humanevents.com/sarticle.php?id=10101&
http://www.foxnews.com/story/0,2933,200499,00.html
Saddams former number 2 airforce man even claims that Saddam had some weapons sent to Syria.
http://www.cnsnews.com/ViewSpecialReports.asp?Page=\SpecialReports\archive\200602\SPE20060202a.html
http://www.nysun.com/article/26514